My computer will not boot unless in hit reset

Hello,
My computer will not boot unless I hit the reset button upon start up. It just started doing this. It will usually be fine after this. Sometimes I will get a message that says that it is stuck in a infinate loop, and must restart. Sometimes I will get blue vertical lines on my monitor and it will not boot unless I go into safe mode. Sometimes it will just shut off. I have a custom built system. It's a core 2 duo intel with a radeon 3850 graphics card 2gig memory, 250 gig hard drive. The monitor and computer are on two different power supplys. Any suggestions?