Screen went blank,dell 1525

Hello,
I have a dell inspiron 1525 and for some reason my computer gave me a blank screen. this is weird i just got this computer and im a virus freak i always scan for viruses and stuff and it wont let me get past the password screen and i dont know what i wrong im freaking out. it wont let me do a system restore or nothing i dont know what to do!! some one help. i was able to get in one time i clicked on something that said internal htt and when i got into my computer i did a scan with avg Free, it said the computer was fine and after that im not able to get in anymore or anything, please help.