While playing GTA Vice City the game locks up and has to be restarted, It seems to do it when there is a lot of action on the screen, and I have been using cheats. What's wrong?

Your disk may be a faulty or scratched severely if it doesn't run at all and the disc stops all movement for ever. Try cleaning your disk by rubbing the inner-edges of it with rubbing alcohol with a q-tip or a cotton swab. Otherwise by a new game. BTW: It could also be a system malfunction or your system is getting to old.

My PC version has never done that but a ps2 version i played did

For some reason, that happens all the time to me. They makers of GTA VC fucked up with the game, and thats why it does that. I just wait, and after five minutes, it goes away. It usually comes up before I do that mission where I have answer that 2nd phone call near the mall. If waiting doesn't work, then you should just restart the game, or buy a completely new CD. That worked for me, and it didn't come again.