FAQ: Will <insert PSU model> Power Supply work with my system?
It's not jst total wattage draw that matters. The Opus 120w can provide up to 42 on teh 12v rail.
The P4 2.4Ghz has a max draw of 57-59w
The Celeron 1.7Ghz has a max draw of 63.5w
The Celeron 2.0Ghz has a max draw of about 53w.
There's your problem!