I have 2 USB key drives, and if I write files to them on one of two computers, then try and read them on the other (or sometimes the same computer) they are sometimes corrupt.

Have you tried the stick in a different computer?
Where was the stick written to?
The first thing to do is see if you can read it elsewhere, copy the files off it if you can, format the drive using windows, check if you can read/write in your computer and copy the files back to it, leaving them as a backup on the other computer in case the stick is faulty
How to Format Flash Drive
OR
There are programs which can sometimes rescue usb stick data but your computer has to recognise that the stick is there. Look in disk management to see if it knows the stick is there. If it is you can use software such as
How to do data recovery from RAW usb drive may cost but is good

Data Recovery Software by ADRC is free

Insert your USB drive in the appropriate USB slot in your computer.
If the Autoplay dialog box appears, select "Take No Action" and click the "OK" button.
Launch your anti-virus program, such as AVG Antivirus or Anti Malware.
Select the USB drive for the program to scan.
Click the "Start Scan" button or option.
Open the scan history for the USB drive when the scan is complete to see a list of viruses and warnings identified by the antivirus software.
If desired, select the options to "Heal All Infected Files" or "Move the Infected Files to the Virus Vault" to ensure these files are quarantined from your system.
Highlight each infected file in the scan history.
Write down the file name of each infected file identified on the USB drive.
Minimize the application's window.
Select "Run" from the Windows "Start" menu. In the Run window, type "e:/" at the command prompt to switch to your USB drive (or type the drive letter for your USB drive).
Press the Enter key.
Type "attrib -s -h -r -a *.*" at the command prompt to remove the system, hidden, read-only and archive file attributes.
Press the Enter key.
Type "del ####.+++" where "####" is the file name of the infected file and "+++" is the file extension, at the command prompt line.
Press the Enter key.
For example, "del terriblevirus.exe" will specifically delete the Terrible Virus executable file. Repeat for each infected file on your list identified in Step 4.
Close the command prompt window; that is, exit the Run utility.
Maximize the window for your anti-virus program (which is still open) and repeat Steps 2 to 7 until no virus is detected on your USB drive.
Exit the anti-virus application.

or Click start click on my computer you should see your usb drive right click then select format.
another way is to control panel administrative tools computer management disk management Right Click on your drive select format

Insert your USB drive in the appropriate USB slot in your computer.
If the Autoplay dialog box appears, select "Take No Action" and click the "OK" button.
Launch your anti-virus program, such as AVG Antivirus or Anti Malware.
Select the USB drive for the program to scan.
Click the "Start Scan" button or option.
Open the scan history for the USB drive when the scan is complete to see a list of viruses and warnings identified by the antivirus software.
If desired, select the options to "Heal All Infected Files" or "Move the Infected Files to the Virus Vault" to ensure these files are quarantined from your system.
Highlight each infected file in the scan history.
Write down the file name of each infected file identified on the USB drive.
Minimize the application's window.
Select "Run" from the Windows "Start" menu. In the Run window, type "e:/" at the command prompt to switch to your USB drive (or type the drive letter for your USB drive).
Press the Enter key.
Type "attrib -s -h -r -a *.*" at the command prompt to remove the system, hidden, read-only and archive file attributes.
Press the Enter key.
Type "del ####.+++" where "####" is the file name of the infected file and "+++" is the file extension, at the command prompt line.
Press the Enter key.
For example, "del terriblevirus.exe" will specifically delete the Terrible Virus executable file. Repeat for each infected file on your list identified.
Close the command prompt window; that is, exit the Run utility.
Maximize the window for your anti-virus program (which is still open) and repeat Steps until no virus is detected on your USB drive.
Exit the anti-virus application.

or Click start click on my computer you should see your usb drive right click then select format.
another way is to control panel administrative tools computer management disk management Right Click on your drive select format

Most of the boot up of problem because of hardware problem, registry missing or crashed, file deleted or changed.
You can boot up your Windows with Tenorshare Data Recovery WinPE.It allows users to burn ISO file to CD/DVD/USB flash drive directly.
Step 1: Download Tenorshare Data Recovery WinPE in any available computer (not from PC that can't boot up). Then launch it.
Step 2: Insert CD/DVD/USB flash drive to the computer, choose ISO image file. Here we take USB flash drive for example. Then burn ISO file into flash drive.
Step 3: Insert the burned flash drive to the unbootable PC. Run computer and press "F2", "F10" or "Delete" to enter BIOS setup.
Step 4: Use the arrow keys to select Boot tab, select Boot Device Priority and press Enter. Please choose 1st Boot Device to USB, and then press F10 to save setting. Now,you can boot up your PC.
If you have a backup for your Windows then perform a system restore to fix it.If not,reinstall it.If you have no backups for all your data,you can use Tenorshare to retrieve data under any boot up problem.You can get it from http://www.any-data-recovery.com/product/datarecoverywinpe.htm
Here is tutorial to guide you how to do --How to Recover Data from Computer Won't Boot Up?-Windows Data Recovery.

connect your flash drive with your computer . then open the my computer . On my computer find your flsh drive then open your flash drive and now copy the documents in the flash drive now open another my computer option then open any of your local disks like local disc c or d or d then now press the following keys at the same time ctrl+v. if still having problem reply me i will help you

The problem might be a loose connection or bad configuration file (an autostart ini file that makes the hard-drive do certain things when plugged in) in the root folder of your hard drive. Are you able to connect to it sometime or it doesn't work at all? If you can read it, try backing up all your data and format the hard drive and copy back the backup again. But remember to copy only the needed files and not the system or ini files.

An external storage-device has four major components:

* the USB cable

* the power-adapter

* the disk-drive inside the enclosure

* the USB-to-disk-drive adapter inside the enclosure.

One of these components has failed.

Try a different USB cable.

Try connecting to a different USB port on your computer.

Try connecting to a USB port on a different computer.

Take a "multi-meter" and measure both the voltage and amperage output from the AC adapter, and compare with the specifications on the label on the adapter.

Open the enclosure, and remove the disk-drive, and then connect it as a "slave" disk-drive in a desktop computer, to see if it works at all.

Purchase a new, compatible, disk-drive, and install it in the enclosure, to "revive" your external storage device.

Get the part-number and serial-number from the label on your disk-drive, and access the manufacturer's web-site, and use "check warranty status", to see if they will replace the device, at minimal cost to you.

Note that W.D. has a "Customer Loyalty" program -- you can buy a new W.D. device, through the W.D. web-site, at a significant discount.

There exist commercial "data recovery" services that can try to repair your device, just long-enough to rescue and copy your files. For example, see: https://services.seagate.com/index.aspx?lng=en-US for a "no data - no charge guarantee".

Try both moving it to different computers and reinstalling drivers.

Most of the Mp3 players do have physical switch to write protect, if you can locate it try to switch off write protect option if not after connecting device check the drive is read only if thats the case anticking read only.