Blank screen on a Dell Inspiron 8500

When I start my Dell Inspiron 8500 I get a blank screen most of the time but sometimes if I let it set off for awhile it will let me in but it is very slow and I can’t open most programs and the screen keeps blinking off and then back on. I ran the diagnostic tests for a blank screen and on the first one I got the beep code 3-3-3, but it just keep giving me that same code over and over. When I pressed the key the beeping stopped but it didn’t do the second test. I ran the tests two more times and I don’t get any beeps. Any thoughts?