PC STARTS BUT NO VIDEO SIGNAL IS PRESENT AT THE MONITOR

I HAVE A GATEWAY 310S DESKTOP PC. IT WAS FULL OF DUST INSIDE SO I CLEAN IT ALL, MOTHER BOARD, CPU HEAT SINK, CD-ROM, HDD, RAM, MODEM, AND THE REST OF THE EMPTY TOWER CASE. WHEN I START THE PC NO VIDEO SIGNAL WAS PRESENT AT THE MONITOR. I CHANGE THE RAM FROM ANOTHER WORKING PC BUT IT NOT SOLVE THE PROBLEM. I CHANGE THE CPU, IT STARTS BUT NO VIDEO SIGNAL PRESENT. I PUT THE ORIGINAL RAM AND CPU AND A VIDEO CARD BUT STILL NO VIDEO IS PRESENT AT THE MONITOR. I USE ANOTHER MONITOR AND THE PROBLEM REMAIN. I CHECK EVERY CABLE AND ITS OK. I EVEN TRY ANOTHER POWER SUPPLY AND IS ALLL THE SAME. NOTE. A RED LIGHT COMING OUT OF A LED ON THE MOTHERBOARD THAT SAYS FP USB WAKE LIGHTS EVERY TIME I TURN ON OR OFF THE PC. IF I TRY TO FLASH THE BIOS WILL IT HELP? OR IS THERE ANOTHE SAFE WAY TO SOLVE THE PROBLEM. THANK YOU!