If what has been suggested (checking for and removing malware) does not turn up any results, and you still want to do a Windows Repair, then you may need to take another approach.

First of all, have you tried what rider_royal said? You may have given admin privileges to another account which you now think is the admin account, but the password you are looking for is the one for the account called 'Administrator' (unless you have changed its name). Attempt a blank password and see if that works - many people forget to password-protect the original admin account.

If it doesn't, and you still can't remember it, then you may need to change the Administrator password. This can be accomplished by using a boot CD like ONTPRE - but please read the instructions and warnings associated with it before you use it. That will help you alter the Administrator password - and then go back into the Windows CD's repair and, if all goes well, you should be able to use the password you just set.

HTH,

-jk