You need to look at your Crtl+alt+del and #1. look at how many threads are running and how much ram & CPU is juked at all time. Click on the Performance Tab
You'll see Physical Mem Total and Avail, that'll let ya know if you need more.
You'll also see CPU usage, that'll let ya know if your comp is overrun.
Most likely its because you have a Dell
(j/k) Really it all depends on how much RAM photoshop is eating up. You probably need 2 gig for that like everyone else says. Turn it off and see if you still have trouble.