If it's the supervisor password that's set, then removing the CMOS battery won't reset it.
I'm not familiar with the 600X, but I'm surprised by the fact that you say you can't get into the BIOS setup even though you know the password? The 600X user guide, (http://www-307.ibm.com/pc/support/site.wss/document.do?sitestyle=lenovo&lndocid=MIGR-4DHV9X
), says to:
Press and hold F1; then power on the computer. Hold
F1 until the “Easy-Setup” menu appears.
If you have set a password, the “Easy-Setup” menu appears
after you enter the password.
If this does not result in getting access to the BIOS (Easy-Setup) menu, then my guess, (from a quick scan of the 600X user guide), is that the supervisor password is set and that it is different to the password that you know
- there are 3 different passwords that might be set, namely power-on, hard drive, and supervisor, (see pages 94-104 in the user guide).
If you are able to get into BIOS setup then just go to the PASSWORD option and set a new supervisor password equal to nothing - i.e. only hit ENTER when asked for the new password. I know this works on a 390E/X.
If you still can't access the BIOS, try powering up with the hard drive removed. On a 390X which had the supervisor password set I was able to access the BIOS setup with just "ENTER" when the hard drive removed, but the correct password was required when the hard drive was installed. The 'catch' was that some BIOS functions were inaccessible unless the proper password was used!!