Since a CPU has no ability to have a password in and of itself (it's just "dumb" silicon) I have to assume you mean that the operating system and/or the BIOS (newer ones are UEFI) has password protection. If the first is the case, you would simply reinstall the OS like you've tried. This makes me think the second is really the case. If your BIOS is the thing with the password on it, you'll have to clear your CMOS, I suggest looking up instructions for your motherboard on how to do this as it can differ depending on the manufacturer. Most of the time you simply need to unplug your computer and remove what looks like a watch battery from your motherboard and let it rest for a few minutes so all residual power is used up. Then you should be able to start the computer back up and you will have cleared out all BIOS settings. Like I say though, make sure you read the manual for your motherboard.