Why, Sims 2, why?

Uhh. Yesterday was supposed to be a good day.
I was supposed to cook my Healthy Yummy Food, eat in peace, write some essays.. WRONG. I spent the whole evening and night sobbing in frustration.

Q: What happened?
A: My graphics card (Radeon HD 3850) arrived.
Q: But isn't that supposed to mean that your Sims 2 works perfectly?
A: Yes, it SHOULD work perfectly. It doesn't.

The thing is, I've had issues with Sims 2 since April. I have all the extensions and the I really like the game. First, the new graphic card Dad installed didn't agree with the game, no matter what we did. I sort-of gave up until December, when Dad came here and installed a new graphic card which proved to be too old and inefficient in order to run the game smoothly. We then bought a very new, cute, supposedly very good graphic card (Radeon HD 3850, as I mentioned) and.. yeah.

C and I installed the card perfectly enough, I later downloaded all the drivers and updates and.. well, all, but the effing game just won't work. My Dad, living 300 miles away, took over my computer (with a cute little progam called TeamViewer) and tried to find out what went wrong.

We got the game working by midnight, but it still flickers and flashes black once in a while. So annoying, and therefore I can't say that the goal #99 would be done. I want the game work like it should work, I just don't know what to do anymore.