dell dimension 4700

I went to power on my dell dimension 4700. I powered it on, It booted to the welcome screen. I forgot the password so i rebooted it and went in to safe mode, The system rebooted half way into safe mode then the system locked up. I pressed the power button for 7sec powered it off, waited 30 sec, then powered it back on. When i powered it back on, the fans were on high and i got no video. I powered off the unit and unplugged it, reset the bios and still, I get no video but I do hear the fans spinning high. What can be the problem? Please post your thoughts! Thanks in advance!