Motherboard problem :( - Please Help :)

[$hadow]

Ok, today I bought a Radeon 9600 XT to replace my old Radeon 9200SE, I turned off my computer, stuck it in and turned the computer on. The computer was running fine, the monitor and keyboard turned on. However, then I turned off the computer and installed a CD Drive (I want to format my computer and install XP, my CD Drive wasn't plugged in). The computer still worked but the XP CD didn't want to boot from DOS. So i went into Setup (the blue screen) and put CD-ROM to be first bootable device, then i went to save and exit. The computer restarted and the monitor and keyboard didn't turn on, but the computer is running and all lights and fans are on (including video card light). I still have this problem, I've tried taking out the RAM, replacing the RAM, replacing the video card (tried 2 diff video cards, no change), I replaced the HDD and I took out the CD-ROM, still no difference. My bro says the mainboard is short-circuited and that I have to wait a few days, but maybe its something else that is more easier to fix. Someone please help .

$hadow

[darkhall]

have you chacked that the drives floppy drives are inserted the right way around

[ccb056]

reset the cmos by taking out the battery with the computer unplugged and put the battery in 5 minutes later, then tell the computer to boot from the cd rom drive