Black Screen After Booting Up Both My Laptop And Desktop

For the past few weeks I have noticed my laptop becoming slower and slower. As of a few days ago it has been ridiculously slow and is sometimes unresponsive to commands or keyboard. It used to go straight to a black screen with only the cursor after start up but now sometimes starts up, although very slow. Now my desktop started doing it too. I don't know what's going on with them. I had not had any virus protection for a while and recently installed webroot complete 2012 on both of them and scanned, finding nothing. My desktop sometimes loads into safe mode when I tell it to, however it still is extremely slow, SAme with he laptop. And if I try to start up the desktop on normal is stays on black screen. I have noticed that sometimes I will get the "Microsoft windows isn't responding" pop up. My control alt delete doesn't work on either of them either, it pos up suing something like " the control alt delete function could not be started blah blah blah".