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Sometimes you can't read floppy disks in your computer's floppy drive.
It can be related with the floppy disk media itself.
But the drive can be misaligned or faulty, too.
If you suspect the drive to be defect, you can replace it (if the drive is still available or can be taken out from an other (old) computer).
You can try to clean the r/w heads with special cleaning diskettes, or may be with cotton buds and pure alcohol. But this helps only in rare cases.

At least you should narrow down what is not working, and if it helps, do something (see below).

So there is a checklist I created:
a) Do your drive have a "belt" instead of a more modern direct drive ?
b) If so (with belt), check the belt. Does it have still a tension ?

c) if you want to use the drive and it has all power connectors correctly connected, does the LED light up if you try to access the drive (regardless of successfully reading a floppy) ?
d) if the LED does not give any sign, are you sure you connected the data line correctly (beware of the old IBM PC drive select crossover cables) ?
e) if the LED lights up but you can't read any sector, did you tried a different floppy disk or may be also a different data cable ?
f) if the LED lights up during access but even with different floppy medias reading doesn't work, did you try to format (if you can boot up with a different drive) a floppy with that problematic drive ?
g) if formatting a floppy media works, but you can't read this formatted floppy disk on other computers, did you're using the right media (DD versus HD floppy disks) ?
h) is the formatted floppy readable but only in the same drive ?



If yes is the answer for a), but b) can be answered with no, replace the belt with a similar, but new belt.

For drives without belt or with a belt with enough tension:
If you answer c) and d) with yes, continue with the subsequent points e) to h), otherwise you are lost and have to replace the drive.
If f) was successful, but g) and h) was answered with yes, you can try to re-align the drive, it sounds that the drive is misaligned. Just take another already formatted and proofed to be good floppy disk, insert this floppy disk, and try to change the position of the r/w head of the floppy very CAREFULLY. During this procedure, try to read the disk continuosly.
For 3.5" inch floppy disk drives, this will work sooner or later, I've successfully resurrected such drives a few times already.

The shown TEAC 3.5" floppy drive is an exception, because the logic board, see red arrows, is already also a mount for the drive head mechanics.

Another example is this drive from Sony, MPF72C-1, used for Thinkpads as an internal drive:

To move the head, just untighten CAREFULLY the one torx screw which holds the plastic head frame. If you move the head, do it in very small steps. One millimeter is very much.

Real "alignment floppy disks" are to be used with additional eletronic equipment like oscilloscopes. You will not have success just with such a media only.

If you're curious what possibilities exists for reading floppy drives, visit the excellent page from code4lib.org, see "related link" below. Try also >Herb's Floppy Drive info collection<.

A real beauty, this IBM PS/2 P70 - a 386 based machine with an ESDI harddrive.

But also a delicate device, because meanwhile the floppy drive often could make problems (can be related with capacitors on the floppy drive board) and also the ESDI drive is NOT unproblematic. If you run SCANDISK (from MS-DOS 6 or later), and if you get after each program run loop more and more bad clusters, you have "disk snow". This means your drive is dying slowly. Also, trying to low level these ESDI drives is NOT easy, you should NOT use drive manager software for this task. There is a special setup floppy disk for this purpose, and there is a secret key for entering the low level format menu (press Ctrl-A within the normal diagnose main menu). But even then it could fail (this happened for my try). Can be related with the "bad sector table" which should be existing for each ESDI drive. Don't know an other reason, because otherwise if the drive controller is faulty, I would get errors while loading/saving files. But all things saved on hard drive works smoothly (no errors). Regardless of that, also the display can make problems.
The plasma display is - if it works - not too bad, see the second picture driving "Pole Position II"...

Last but not least the keyboard is excellent, similar to the famous "clicky" IBM PS/2 keyboards for the IBM desktop computers (but a bit more compact).

See "related link" for a related site / a source for the setup & diagnose disk for the P70.

Very nice, and runs with CGA, EGA and VGA cards: Sargon 4 (and not Sargon IV), distributed by Spinnaker Software, not from Hayden Software (which published the famous first three Sargon versions). It's playing good, although different from Sargon III, which is not surprising because it's from a different software developer.
It looks in all three possible display modes good, see yourself:

CGA

EGA

VGA

See wikipedia also for additional infos about the Sargon series (related link below).
Other chess programs are shown and listed in my 4 part blog series, --> last part here

Yeah, hate this. While I tried to copy Kaypro II floppy disks in my PCs (with TELEDISK first, but then with 22DISK, and with many read retries), I thought it would be much easier to copy them with my Kaypro II itself. Just power it on, boot with CP/M 2.2, start COPY, and then the copy session for about 10 disks was started.
But guess what happened - it makes an ugly "Poff" sound and then it stinks forbidding.
The capacitor for avoiding interferences from the power supply line, a 0.22 uF "film" one, exploded and burned a bit too. I switched immediately the computer off and carried it to outside the house (... still stinking).
Then I opened the case, dismounted the mainboard, then the power supply itself:

This was the capacitor after explosion:

After I buyed a new capacitor and after repair it looks now like this:

And after reassembling most of the parts, it runs (without stinking) again, hurray:

There were some other capacitor candidates for a later replacement, but I was happy it runs again.... the Kaypro II and its power supply was MUCH EASIER to repair compared to the nightmare with the Macintosh IIci. See "related link".

These advertisments in the eighties were not very plausibly, but not only IBM published PC Ads in that manner. That man couldn't really look onto the screen and was able to read anything. See and judge for yourself:

But it was IBM's necessary answer to the Compaq Portable PC, a bit late, yes.
And it's a beauty meanwhile. Other portables looked more ugly.

Corona Data Systems and also Sperry Corporation (in fact, it was the same computer with different labels) selled early portable PCs. This is a picture of the "Sperry Portable Computer", which is meanwhile a real rare Portable PC (still looking for an affordable one):

It was selled from late 1984 until Sperry Corporation was merged with Burroughs in 1986.
It doesn't have an amber screen (like the IBM Portable PC), instead, a green one with 9 inch size. An Intel 8088 with the same speed like the first IBM PC and 256KB RAM (expandable to 512KB on motherboard) was included.

See also in related link for an article in "Infoworld", November 1984.