OK, some background. For the last 6 months I have been running an Athlon64 3000+, 512MB 7900GT, 1GB RAM, 2 HDDs etc. from a crappy 350W PSU that came free with a £25 case 4 years ago.
No problems with stability, but recently the noise of my PC has been starting to bug me, so I bought a new PSU, heatsink/fan and case. The new power supply is a Seasonic S12-430.
I hooked everything up (built about 5 PCs now so getting quicker) and when I push the power button, the fans spin up for a second or two and that is it - nothing on the monitor.
After messing around pulling out components etc, I tried with my old PSU and instant success. This is a PSU with a 20-pin power cable and a 24-pin motherboard but still it works better than my new Seasonic.
I'm pretty pissed off right now so I'm going to bed, but I thought I'd post here and check any replies in the morning. Any ideas? Dead PSU?
Sorry for the long post.