HP pavillion 4540

I picked up an HP Pavillion 4540 at a yard sale for $3.00. I asked what was wrong and was told that it kept saying press any key. When any key was pressed it would reboot and say the same thing. I took it home and plugged it in. I can’t get past theHP splash screen. It does not go to POST. I thought it might be the processor and got another one that I knew was good. It still won’t go past the HP splash screen. When I boot it up, I can hear the hard drive working but that’s as far as it goes. Any suggestions????

Lynne