HALP Any ideas

[Mikaelo]

At random times my screen will turn into a weird blend of colors of whatever is going on on my screen. It looks like if you took the colors on my screen and then threw up all over my screen. When this happens my computer just locks up and I have to power it off from the case. Sometimes when I try to start it back up my motherboard wont POST and I have to shut it off and back on again. There doesn't seem to be any type of consistency when it happens, it has happened when I'm idling, when I'm in a game or watching a movie. Sometimes when I turn my computer back on even my BIOS and/or windows XP loading screen is fucked up (part of the screen is just tiled everywhere). Sometimes it happens 3-4 times consecutively within 5 mins of turning my computer on then it wont happen again for hours. This just started happening when I unplugged all of my components to clean the dust off stuff so I thought maybe I didn't plug something in all the way or something that wasn't suppose to be touching my motherboard/case was touching it and shorting it out but I've reconnected everything and cable tied everything so its neat and nothing is touching something it's not suppose to. I'm stumped and it's really annoying, anybody have any inch of a clue of what is happening?