Blank monitor on startup. Might be a BIOS issue

First off, thank you for reading.

So my PC wasn't displaying anything on startup. I swapped out the monitor, which solved the issue, and called it a night. I come back the next morning and yet again the monitor is going blank soon after starting up. I can't get passed the initial screen with white lettering.

The first error I received was "Warning! CPU has been changed or CPU ratio change failed. Please re-enter CPU settings in the CMOS setup and remember to save before you quit." Attempts to go past this with F1 or to enter Setup with the Del key were met with a blank screen. So I pulled the CMOS battery, let it sit for a few minutes, and put it back in.

Now the error I get is "CMOS checksum error - defaults loaded." Yet again, F1 and the Del key will only bring me to a blank screen.

I've also tried resetting the CMOS jumper, which leads to the same results.

The CMOS battery isn't dying - I've tried swapping it with a new one and it didn't help anything.

I'm running XP Pro SP3.