OK, since you didnt list your vid card, I'm just going to toss out a few things here...
If you have a newer card (geforce 3 or 4, ati radeon and up) did you install the latest version of directX, and then the latest version of your driver? When you install Windows from scratch, it most likely wont detect your video card, unless you have an older one. Just DONT use the drivers listed on Windowsupdate, if it offers any.
Since you are also having the reboot problem, try starting your machine with the bare minimum of components. Start with your processor and ram and a video card (maybe even try a pci card if you have one). No network card, no sound card, etc. See if you have reboot problem. If not, then go ahead and try adding things back in.
You said its a old rig with a new hard drive...the parts you listed look pretty new to me, so Im not sure I understand what you mean.
Also the next time you get it to boot fully (in vga mode or otherwise), log in and check the eventviewer...go to start|run and type eventvwr and tell me if you see any suspicious reds or yellows.
The parts you have are pretty standard, nothing weird here, so its possible you have a bad part, maybe memory...something to think about
good luck