I bought some new PC parts on Saturday... Plugged it all in, turned PC on and installed Windows XP.. Easy...

Then I decided to plug in my Old HDD, DVD drive and some funky lights...
I plugged them in, turned PC on.. and nothing.

There was power going to the mobo/gfx card etc (I know because I heard the fans etc, and saw the lights/lcd screens on mobo) but nothing appeared on the monitor.

I took out all the power leads, and ONLY plugged in the GFX card (its PCI-Express) and the primary HDD.

I thought this should work, because it is now the same as when it worked... But it didn't... Still nothing appears on the monitor..

Help!

(7800GTX PCI-E, Fatal1ty Abit AN8, 160 SATA HDD, 550WP PSU)