Vista - vista screen goes blank white

after logging on to my name the screen just stays blank this is what happened right before i turned it on.

i have a hp pavillion desktop running on windows vista home premium. okay what happened was i went to the switch users area and left when i came back i couldn't do anything i tried to sign on but nothing happened there was a bar that said switch users when i clicked it nothing happened so i tried to sign on my name again and it said something like this " There is device attached to your computer that isn't working". so i decided to restart my computer when i did this a black screen came up and said something like this " removing security something # from id" than " replacing security# with #" than it restarted and i signed on but a white screen came up and stays white