Dell dimension desktop 521entertainment center 2005 crashed wont recognize resou

what to do

When you say crashed - what do you mean? What were you doing at the time and how did the computer behave - what were the symptoms?

Had you made any recent hardware or software changes?

What exactly do you see and hear when you try to boot the system?

What if anything have you tried this far to get it to boot?

Please post a link to system specs (you should be able to find this at Dell support if you have not already copied it) and ID any changes you might have made - such as adding more RAM or a different graphics card.