dead pc

I have a dell PC that has been acting up and crashing. I was going to back up my info on a usb flash drive. I plug in the drive and get the blue screen. Reboot. I log in start to copy to the flash drive, came back in a few minutes and the screen is black and the keyboard isnt responding(num locks, cap locks is staying off) So I had to cycle the power and now nothing is happening. The monitor isnt getting a signal, keyboard wont respond but the cd will spin and the hard drive will spin. I am not getting any beeps either even if the drives are unplugged from the MB. I am thinking the power supply, MB, or processor went. Any tips?