I'm embarrassed to say the type of laptop bec. of its age, but I only paid $100 for it.

It's a Dell Latitude D600 and the graphics sometimes (like now) and basically any time it's cold outside (temp inside is 66 F but it seems to do better at higher temps) freak out. Anything that's supposed to be black is fluorescent green. Makes for a great video - NOT!

I've done the corner to corner twist sort of test on the lcd screen, and nothing changed. I've read a couple other things that might be the source, but I never asked for myself, so here I am...

I'm not going to open this thing up unless one of you walk me through it step by painful step. How much should it cost to fix bec. I don't have the money for a nice, new one, and I need this for school.

Oh yeah, I'm a near total electronic retard. Be gentle and type very, very slowly, please. ;-)
Thanks in advance!

Try giving the chassis of the laptop a gentle twist to see if that makes any difference!
I suspect you either have a ribbon cable fault (the cable that connects the screen to the rest of the lappy) or a poor solder joint in there somewhere.

If it's the ribbon cable, it can be replaced reasonably cheaply, if it's a solder joint then it will need to be reflowed which is a big job requiring specialist equipment!