Dell Dimension 8400

Power button flashes, nothing else comes on

is it orange

if its orange then its a power supply...

I would start with the power supply. Looks like any standard atx ps should work. Pc power and cooling makes a dell replacement 500w silencer for $79.99 at newegg. Or, you can try antec, another good brand I use. If a new ps doesn't work, then it's time for a new pc, if you don't want to build your own. The 8400 board is priced at $119.95 at 2 places (one new on ebay). It's not worth putting that much into an old motherboard, when you can sometimes buy a new dell vostro for around $450 which often includes a monitor. I found my compaq new for only $199 last year at Fry's electronics.