You may want to try the following to see if the motherboard is shorting out on the case:
Find a cardboard box that is at least the size of the motherboard, if not bigger. Place the board on this, making absolutely sure that there's nothing that can conduct electricity on top of the box! Install your RAM, CPU, heatsink and anything else that you need to get the motherboard to boot up (unless you have those parts already installed).
Connect up the power supply, make sure that there's no cables anywhere near the CPU fan

Attach the hard disk and CD-ROM drives, check the cables from each for any creases, breaks, bends or fractures.
Now, this is the tricky part. Examine the motherboard manual, and find the two pins that are for the Power Switch. Using a flathead screwdriver, touch the two pins together.
Be very sure not to touch anything else with the screwdriver!. Use two hands to make sure you're steady if need be.
The system should now be on and running (if not, double-check the manual, and that the power supply is indeed switched on). Have a go at installing Windows again, and if it works, then your problem is that the board is shorting on the case, or something else. This should at least give you some idea if this is the problem or if something else is wrong.
If you hit any problems, or have any form of success, then please post back to let us know
Good luck!
[Edit] Don't worry about the red washer insulators too much, I use them by putting them over the top of the screwhole and then passing the screw through them, so they're on top of the board, not underneath. However, I've built hundreds of systems that don't use them, so they're pretty much a moot point.