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#51
I would read the motherboard manual and do a reset (usually involves moving a jumper on the motherboard). Then, I would install one RAM module and your video card (if you don't have onboard video). Boot and see if the BIOS starts. Load failsafe defaults, then reboot. Enter BIOS to verify it works. Shutdown. Install the other RAM module, boot and verify you can enter the BIOS. Shutdown. Connect only your DVD, then start the computer. Verify you can boot and you get a message about a missing OS/media/etc. Shut down and connect the hard drive, and repeat the above actions.
Post your results.
In the meantime, verify the RAM you bought is compatible with your motherboard. Also check for any BIOS updates, and if you find one, download it to a flash drive and follow the BIOS update instructions in the motherboard manual.