While playing some games screen keeps flashing off after a USB input sound?

[PieClock]

For the last week or so I've been having a problem during playing some games (such as Dead Rising 2, and GTAIV). The problem starts out with me hearing the sound that plays when you put in, or take out a USB device, then a few seconds later my screen will go black, and a few seconds later come back on. After this does this once it'll do it about 30 times before stopping for 5-10 minutes then it'll be back again.

This problem seemed to start after I opened my computer to get some measurements the other day, so I'm thinking I've knocked my graphics card loose. What would be the symptoms if this happened? Would it be similar to what I'm experiencing?

If not, anyone got any ideas what could be causing this?

[djjkxbox360]

I'm guessing if you take the graphics card out whilst Windows is running that would happen, however it's not a very normal thing to do. I'd open the computer up and make sure nothing is loose

[PieClock]

I guess I'll take a look; I'm upgrading it next week anyway. Still doesn't explain why it only happens when i'm gaming though.