Won't boot but PC powers up

Hello,
My computer recently decided it didn't want to boot up. It was running fine when I opened the case up to see what memory I had installed when I built it 3 years ago so I could add more. I put the side back on and rebooted because the network cable had come undone. Then it gives me the message about normal start or safe mode,etc. I hit start normal. Then it frezzes as Windows is loading with that little led looking graphic going back and forth. I reboot again. It gives me the option of normal or safe mode again. I hit normal and it gives a message about something changing and I need to install the Windows cd. I changed nothing. I didn't even remove a part. I just looked to get the part number off the ram so I could get more of the same. I rebooted again and this time the red light on the front comes on(stays solid as long as it's on), but the cd roms don't power up and no video/no signal to monitor. I uninstalled the video card..nothing..hd..nothing... eraser trick on ram and reseat..nothing. try one stick at a time in different slots..nothing. all fans and lights power up. I don't have my speaker hooked up so I don't know if it's beeping or not. I built it and it ran for 3 years so I have some experience but this is new to me. Any ideas?

System consists of:
Gigabyte DS3 board
2.66 Core 2 duo
2 gb ram
WD 250gb HD
dvd-rom
cd/dvd combo
evga 512mb pcie video
NZXT 550w psu
Vista Ultimate 64