sims2 crashes...help?

my game has been randomly crashing, i don't know how long. it has a couple ways of crashing:

ONE: my game will freeze and the screen will go blue, sometimes moving my mouse around helps it not to crash, but from there it will normally restart.
TWO: the game will crash, the music still plays, the cursor is still moveable, the game looks as if it is paused (but now red outline) nothing will help except restarting. no ctrl+alt+delete, or alt+tab.
THREE: the game will crash, my moniter will go on standby (normally the light is solid green for on, and blinking yellow for standby.) but i can't get the moniter back on, and it plays the same sound randomly over and over.
FOUR: an error will come up, saying the game has crashed and must be terminated.
FIVE: this isn't crashing, but a lot of the time my video card (i guess) has a window pop up saying something about my video card crashed, and had to be restarted, but it doesn't seem to bother the game at all.

these occur randomly, and only during game play, not while loading or anything like that. sometimes it gets the blue screen if i move around to fast, or am going between live, buy, or build to quickly using the keyboard shortcuts.
today it's at it's worse. i can't even play one sim day without it crashing in either of the many ways. it is driving me crazy, and i am in the middle of a challenge, and it's very annoying when i have to restart, wait for it to load the game (it takes forever to load the game, but not as long for a neighborhood or family. depends on when the last time it was accessed) and replay what i have already played a couple times today until it crashes again.
i have the following games installed: the sims 2, university, nightlight, ofb, pets, seasons, bon voyage, family fun, glamour, and h&m. no background tasks, except for an internet explorer sometimes (i used to have windows media player, but that seemed to crash it more, so not anymore). no viruses, i run a scanner at least once a week, and anything else you need to know just ask.
oh, and i have a small fan running, blowing at my computer. it seemed to help.