Booting a new motherboard I installed recently...

if you have changed the motherboard without either re installing windows or repairing windows you will need to because of hardware serial numbers that windows checks against installed hardware.

Change the first boot device in the bios F2 or Del on boot up to your cdrom save and exit and then insert the cd before you re boot.

Allow the cd to install the installation files, but when prompted instead of pressing enter to install windows, press 'R' to repair instead, at which point your C: drive will be shown, press 'Y' to answer yes to the c drive that needs to be repaired and press enter and allow a system repair, no docs or files will be lost as you are only repairing not formatting and installing.

If you have already done the above or done a clean install, check in the bios (F2 or Del on boot up) again and see if all your hard drives and cdrom drives are listed correctly, if not select F10 or F12 depending on bios type, which is normally auto detect drives, as you may have faulty or damaged system files or damaged sectors on you hard drive.

If you get running you right click on your hardrive and select explore,right click 'C' drive, then properties, then tools tab and select error checking.