|You probably replaced the motherboard for nothing. I don't know why people start swapping parts out instead of performing logical troubleshooting.|
First thing to do is to test your memory by booting to a memory test program. Download memtest86+ from the link below. No errors are acceptable. If you get errors then try running 1 stick at a time in the first slot. Snap it in and out 4 or 5 times to burnish the contacts.
Then run a hard drive fitness test for your brand and model drive. Get that from the drive makers site.
When installing Windows you should not have any unnecessary external hardware connected. Webcams, printers, scanners, flash or external drives, etc. Use a wired PS/2 keyboard if you can. USB keyboards may not allow you to access the BIOS screens.
Are you sure the motherboard, CPU, RAM are compatible?
Are you sure you applied the thermal paste or pad the right way?
Next time you boot tap the del key and enter the BIOS immediately. Check the system and CPU temperatures. You should also lookat the 3.3V, 5V & +12V values. They should all read +-5% of the default values. Post your results back here.
Also post the brand and EXACT model of your power supply.