|Not enough details. Not sure what the tab has to do with repeating.|
Try another program to make sure that the problem is not with the program (Word, Wordpad, Notepad, etc.)
If you are having trouble with a keyboard, try another one.
If this is a laptop, an external USB one will work to test it.
If this is a desktop, try both a PS2 and USB keyboards to eliminate possible port problems.
You have to be a little bit crazy to keep you from going insane.