Is it a Brand PC or someone built it?
If Brand, put in the company that made it and model, if built by someone else, then we could use power supply information.
Also pulling the motherboard information
Newegg.com - BIOSTAR P4M900M4 478 VIA P4M900 Micro ATX Intel Motherboard - Intel Motherboards
You will be needing some updates, may I ask what your current budget is for these planned upgrades?