So I upgraded an old p4 for a celeron duo core [E3300] and I installed it. But when I start, nothing comes up on my monitor. It sounds like its running just fine, and I tried clearing cmos and that didn't help either.. Any ideas?
You need to identify your motherboard.
Reinstall your old processor and run CPU-Z which will tell you what motherboard you have, it's revision level, and it's bios level.
1) verify that the E3300 is supported.
2) see if there is a bios update that is needed for the E3300. This is often the case.