1. Change out the card with another known to be working and see if the problem remains.
I don't think that can an option, you see, I only got one graphics card at my place, and to replace that with a working one, I'd have to buy another graphics card. Which I think my dad wouldn't be surprised that I "killed" the current graphics card.
2. Check to the power supply for adequate 12volt power delivery- via a hardware based tester is best. Software based testing requires a BIOS that monitors psu voltages, or a software that can be used in an OS enviroment (like OCCT, Speedfan).
I can use Speedfan for that can't I? I mean I got Speedfan but I don't
really know how to use it....

When I first loaded up Speedfan, I notice my GPU core temperature was over 3 million degrees Celsius! What the F--! Okay, I think, that's to say my graphics card is f******, right?
3. Was the card artifacting prior to the driver install/reinstall -this is a biggie, as it would indicate that the card in cooked. I would be surprised if you ran GTA:SA in modded form without it artifacting to be quite honest. A 256Mb card with limited shader/pixel pushing capabilities being worked in such an intensive game. Just how prevalent the artifacting was and whether you combatted it by dropping some of the mods, or by some ineffectual means (raising clockspeed or dropping to 16 bit colour).
While installing the drivers manually, there was, but this was in normal mode, safe mode didn't show such things. (that's how I installed the drivers)
My graphics card was actually pretty good at rendering the images, at an average of 60fps, you'd have congrats for that! (Tobe honest, there wasn't much graphical options to turn off or on anyways) I myself, don't really think GTA SA is an intensive game, if it was, then running the game with the level of graphics the same will drop down to 20fps or less to be called intensive.....just like running NFSPS, just only the graphics of the car all the way up and the world detail all the way up, it runs just less than 20fps, that's what you call an intensive graphical game!
Anyways, I just reinstalled GTA SA, so everything should be back to normal, car sounds, graphics of the cars, lights, cars and the speedometre I stuck in is no more, I'll just delete the CLEO library for now....Oh wait, I don't think the speedo metre has anything to do with the graphics card, does it? only tells you how fast your vehicles are going and that's all, so, I'm going to leave that in, okay?
If you say my graphics card is "cooked" than, how come, I can still see stuff on the monitor without the drivers, huh? Or is this the doing of the VGA controllers XP gave me? if it was "cooked", I'd see smoke coming out of the tower.
4. If the card will not accept a driver then you cannot test the card by downclocking the core and vram. Which leaves you option 1 or 2.
I haven't down clocked my graphics card yet....so I'll skip this one