After reboot I am not able to run Windows normally. When I log in I can only see wallpaper and nothing else. It is like explorer is not starting. I do not know how to start it manually and I can not work with system like this. Can you tell me what to do to solve this problem?
It looks like you have been infected by WORM_MYDOOM.B. Infected computers show the same behavior you have described above. You can start explorer manually if you wish by following this procedure: press CTR+SHIFT+ESC to start Task Manager and then choose New Task from File menu. In Create new task dialog enter WinDir\EXPLORER.EXE and click OK. When explorer starts you can do full system virus check and delete offending viruses.