I have an old Compaq desktop laying around the house. It is a compaq presario s4000v. It does not turn on. What should I do. Could I buy a new power supply or does it need an older power supply. If that is the problem. I did take it apart, but this is after I couldn't turn it on. Should I try putting it all back together to see if that solves the problem. If not should I buy a new Power Supply. Any input is awesome. Thanks!