Computer screen goes blue and restarts itself?

Yesterday i installed kaspersky 2012 free antivirus and tried to scan one of my drives but it hanged after 1% scan was complete. I turned off the system directly using power on. When i restarted it showed that there is error in the drive which i selected for scanning. The windows resolved the error and was able to access the files and i uninstalled the antivirus. When i restarted the system it showed that there is error in the same drive. Check disk was completing the first stage checking but used hang at the second stage. I changed the ram slots but it did not work. I restarted the system and Suddenly the screen started showing blue screen and started restarting. please help me. I have very important datas that i dont like to loose it. i just want to recover the data. After that i can format the hard disk. But i dont know how to recover the data since i am not able to access the windows.