After recieving a virus depending on its nature, the virus itself could do some considerable damage to essential files needed for your programs and operating system to function properly! I recently obtained my first virus after more than 15 yrs of using the internet. The virus I had was called "LiCum" virus and what it did once activated was it searches your harddrives and infects and destroys all .exe (execution files), which basically begins to make all software unusable, eventually windows itself will not even load anymore once it gets to that point. What I would do is create a "Bootable" antivirus disk and thoroughly scan the drive, remove any further traces of the virus/malware, as some files maybe permanently damaged you may have to re-install those applications, another thing you can do after the scan is to revert your harddrive to a point in time "Before" you recieved the virus/malware using windows "System Restore" assuming you havent disabled it! If all else fails then you will need to back-up your important data (scanning all files you backup to make sure they are not infected) and reinstall your OS and any software you use. Theres alot of software out there to assist you in virus removal, but if essential files are damaged theres not much else you can do but to redo your whole system so to speak! Further advise make sure you "Disconnect" the infected PC from your network until the problem is resolved!!! some forms of Viruses/Malware can search your network an begin to infect your other computers and you Dont want That!!! A major key that most people misunderstand is to have a "software firewall" configured on your system as well as "Antivirus".. Firewalls will help a great deal in blocking and preventing viruses from getting on your system, if you screw up and open one by mistake then hopefully the antivirus software will catch it and get rid of it before it does any damage.. I use "Outpost Firewall" by Agnitum, and Avast Antivirus, I choose these to as they dont use up excessive background resources and slow down your system like Norton, McAfee, and some other "popular" utilities do..! any further questions feel free to email me!