Jenny,would this help,part# 308437-001
That's an old style ATX power supply -
1 X 20-Pin Motherboard Connector
5 X 4-Pin Molex Connectors
2 x SATA Connectors
1 X 4-Pin Motherboard Connector
2 X 4-Pin Floppy Connectors
Almost any standard ATX power supply should fit, but depending on what's wired to the cables you may have problems finding a replacement. How many of the 4 pin Molex connectors are plugged in to devices? Are the Hard drive(s) SATA or PATA?
Since it's an older PC I wouldn't spend too much upgrading it - take a look at something like this as a place to start. RAIDMAX RX-450K Continuous 450 watts ATX 12V v2.3/EPS 12V Power Supply
Being that it's a Compaq, it's hard to say if it'll be a perfect fit.