My computer screen wont turn on

Hello, im kevian

When i turned on my computer it booted up normally but then once when i sign in it deleted everything on my desktop and then it gave me a black background and a windows xp mouse cursor.Ps im on windows 7 home premium.and now every time i turn on my computer it gives me a blackscreen and i tried unplugging the battery and holding it for 60 seconds .it worked once then i tried to reboot it and it still doesn't work.please help