1 beep is a BIOS ROM failure. The other problem is more concerning. The blink code indicates a Memory DIMM Power Rail Failure. And since you stated that the PSU works fine in another system then that only leaves the MB as the source of the problem. Combined with the fact that you had an incoming power event, I would say the MB needs replacement. As far as the Cognizant screen is concerned, you did state that the system does not boot at all correct? Then you cannot be seeing any display that the PC is sending to the monitor. You obviously will not see a DELL image if the system cannot boot. Do you have the monitor connected to any other additional source?
my DELL OPTIPLEX 3020 is not booting since last 1 day. their was a power cut which made it turn off while i was gaming on it, then when i tried turning it on again the desktop's power indicator showed up orange light followed by white light and also made beep noises. then again when i tried to turn it on the extender sparkled. then i tested the ram which is working , power supply is working , motherboard (cognizant) is also working fine. i dont think the graphic card is corrupt.help me soon  thanks in advance
DELL OPTIPLEX 3020 shows orange light and white light (also maked beep noises) 
and does'nt turns on.