The PSU is the Corsair HX620w
It only has 2 PCIe 6+2 cables.
Besides GPU's the only investment is the PCIe risers and a workbench or materials to make a custom one. Only other thing I would have done with this HP was dedicate it to lower end requirement games with my old GPU in it to save storage space and registry clutter on my main computer. The HP locked bios holds it back from performing well as others still running this. It's why I would rather buy someones old computer on reddit hardware swap for low end games instead and turn this into a miner.
I won't be able to buy GPU's until September so I can decide later what to do with this
LGA 775 mobo will not hold back mining performance, I currently use lga 775 and core 2 duos for my mining rigs. I also game on a lga 775 quadcore machine that is stock clocks and I really don't notice a bottle neck, well the games have stunning visuals and great fps. I have 2 cards in a lga 775 "daily driver" machine, I keep one mining and the other is for gaming..still works great.
Don't listen to some of these people, they just have the idea stuck in their heads that old hardware is junk. Not true.
For mining the computer cpu does NOT do the work, the gpu does all the hard work and the main system will just be chilling out waiting to send a little data packet to the pool when it finds a share.
The CPU in this HP is a Q6600, 2.4 ghz quad core. I've looked it up before. Running with good GPU's it loses 10 fps on newer games compared to people with the same GPU on i5 and i7's even though the GHz is met. It's usable of course and running a good GPU will still play smoothly but the legacy is ceeping up