If the monitor picture gets all shaky, it could be from interference nearby that just builds up the longer you computer is on. Try pressing the Degauss button on it (if it's a newer monitor, it'll have one), or move your speakers away from the monitor.
Chances are, the problem is with the monitor, especially if it won't even turn on... unless you're one of those gay people who just flicks the power bar switch to turn everything off.
