That's odd because the exact same thing happened to me a month ago.
Inside the powersupply.. there were 3 blown caps.
On the motherboard.. there were 7 or 8 blown caps.
All of them I desoldered.. and replaced bigger ones in...
Alright... then I found out that there were 3 MOSFETs that were completely fried...
I tried looking around but couldn't find the part anywhere..
so I ended up having to get a new motherboard....
Whatever caused it also took the video card with it, so, to save money, I bought a new motherboard with built in video (not much of a gamer.. so it really didn't matter to me o.O)
It's annoying having to install XP over again.. losing all your old settings (as is with installing new motherboards), all the programs were already on the hard drive though.. which was unaffected.
Linux still ran perfectly.. but XP just begged to be reinstalled with the classic Blue screen of death.
So yeah.. it can't be helped.. exact same symptoms over here too.. the lights were on.. the CPU fan will twitch... you gotta get a new motherboard
I didn't have to replace my power supply though.
(if anyone knows what caused this meltdown.. I would like to know.. I left my computer on.. went and took a shower, and when I came back, it was off and wouldn't turn on again.)