Tools required
1.restriction removal tool
link: http://www.softpedia.com/get/Security/Security-Related/RRT-Remove-Ristrictions-Tool.shtml
2.unhackme
http://www.greatis.com/unhackme/download.htm
3.hijackthis
http://filehippo.com/download_hijackthis/
http://www.download.com/Trend-Micro-HijackThis/3000-8022_4-10227353.html
4.process explorer
http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx
If your pc is affected with some virus the most common of all is your folder otion will be disabled,you may not be able to open task manager, etc etc..
now 1st step is to identify the virus process
process explorer will help u and u may see the path of the installed file on ur system
now use restriction removal tool to remove the task bar ..folder option restrictions...etc...
now our aim is to remove the running virus process..
use hijackthis and select the virus process. it will remove the process from startup registry also..
finally try unhacme.. to remove the rootkits
many virus can be removed in this way but many still remain on ur pc.. in such situations.. try to google for its removal methods manually.. once the restrictions are removed u may be able to use taskmanager and able to use regedit command