I had an unusual happening on my PC. First noticed some instability while trying to open a file from Explorer, could not scroll down to file and it was jittery. Then, every time I tried to enter on an input line, an endless string of zeros were input and I could not overide or erase. Even on Email addressees. I tried a reboot and the zeros appeared on the start up password line and I could not logon. Same thing after complete power cycle. I suspected a stuck key on the keyboard and tried a different keyboard but no help. So I tried a complete restore. At first, it seemed to have the same problem, but somehow, eventually, I got logged on and now everything seems OK. But I don't really know what caused this and fear it could happen again. Virus?? or something. I have Norton.