i was installing an application using ubuntu software center and screen went blank i waited a while but nothing appearing no desktop so pretty much expected result is that i rebooted manually please correct this or tell me what should i do,iam not running any screensavers nor does the virtual console work
Just press ALT+Pet Sys and type slowly REISUB, one key at time. If it happens often you should probably investigate why is it happening. Ubuntu (and linux) is supposed to be rock-solid because it's usually rock-solid ;). This behaviour is anything but normal.