Computer Randomly Changes Monitor Works

I don't know what is going on. I updated to Windows Vista from XP about a week ago. Installed all my drivers and everything worked great for three or four days. But, all the sudden and for no reason at all I woke up one morning and only had one monitor able to recieve a signal from my computer. I checked all my connections, checked all my equipment to make sure nothing was broke, updated all my drivers.

Now it's just funny. When I restart my computer sometimes my computer randomly changes which monitor works. Sometimes both work fine, sometimes both work but they're switched (it thinks the second monitor is the primary and vice versa). Sometimes both will work fine until I do something, for example if I'm browsing the internet and I click on a random link a monitor will just lose signal. Sometimes they both lose signals.