If you aren't able to successfully boot into Windows, then you've likely pushed your overclocking just a bit too far.😁
At that point, you’ll need to start adjusting your Vcore, Vdimm, and various other voltage settings to find that sweet spot.😁
Provided that your temperatures are looking good, you should feel free to push further.
However, if they're already creeping up a little high, it might be worth investing in some extra cooling solutions.
For your graphics card, you can handle the overclocking using tools like RivaTuner, ATI Tool, or similar software.
If you're still running the stock cooler on an X1950GT, would it be a good idea to swap it out for an S1? I certainly think so; it should keep those temperatures remarkably low.
Well, if you don't quite know your way around the BIOS yet, there isn't much else to be done!😂