If you can access the internet, start at step 1. If you cannot access the internet on that pc you can try running Windows Defender, however this is unlikely to find anything. You could use another PC to download RKill, click save and use a memory stick to run it on the infected pc.
1) Run "RKill" (https://www.bleepingcomputer.com/download/rkill/). This program will look at what is running on the system and if it finds anything it will close, but not remove it. Rkill will then let you run other programs if a virus was blocking them.
2) Run the free trial of Sophos Hitman Pro – https://www.hitmanpro.com/en-us/hmp.aspx – this runs multiple antivirus scans at the same time, and finds a lot of malware.
If Hitman Pro will not run, or you still cannot access the internet follow http://www.antimalwaresoftware.nl/handleidingen/hitmanpro-kickstart-user-manual-guide/ from a clean computer.
3) Run Malwarebytes Anti-Malware – https://www.malwarebytes.com/mwb-download/thankyou/ – Malwarebytes is consistantly recommended, it is a very powerful tool and it should be kept installed after it cleans up.
4) Run ESET Online Scanner – http://www.eset.co.uk/Antivirus-Utilities/Online-Scanner – this is fairly powerful and should root out anything left on the system.
5) Run Norton Power Eraser from https://support.norton.com/sp/en/us/home/current/solutions/kb20100824120155EN_EndUserProfile_en_us
If these do not find anything try running ADWCleaner from https://www.malwarebytes.com/adwcleaner/ – While this is from the same website as Malwarebytes it is a slightly different tool.
Then run Junkware Removal Tool from https://downloads.malwarebytes.com/file/jrt/ – this will appear as a black box with white text, and you'll need to use the keyboard to run through it, this tool focuses more on annoyances rather than malware, but still cleans the system well.
If nothing as been lifted go to a site like bleepingcomputer.com or spywareinfoforum.com – these forums have dedicated malware removal guides.
If all else fails back up your files and reinstall Windows.This should cure the problem if you install a new antivirus program and Malwarebytes and scan the backed up files before copying them back.
After your PC is cleaned you can avoid infection in three steps.
1) Update Windows, Firefox, Chrome, Java and Flash regularly. A large number of viruses get into out of date computers which either have Windows Update switched off, or are running an old version of Windows such as XP. The programs listed are also frequently targeted, when these programs ask to be updated do so on the same day.
2) Replace your Antivirus program. I recommend Avira, Panda or Sophos Home. You can skip this step if you chose to buy a Malwarebytes licence, but the free versions of these programs do a good job on their own. (I use Sophos, and this does a good job of blocking viruses before they can infect the machine) From experience avoid McAfee and Avast did a poor job, however I believe that Avast has improved since I last used it. Microsoft's Windows Defender and Microsoft Security Essentials do not protect your computer well, and shouldn't be used.
3) Keep Malwarebytes as a free program. When the trial ends it will turn into a program that needs to be updated and run by the user rather than automatically, essencially a cleanup rather than protection tool. Malwarebytes is very powerful, usually Malwarebyes will be able to clean up any infection your Antivirus misses.
Change the password on your router.
Turn off file sharing on your pc;
Go to the Control Panel – Network – Internet – Network and Sharing Center
Choose Change Advanced Sharing Settings
Turn off file and printer sharing, network discovery and Public folder sharing
– Go to Start – programs – accessories – system tools – system restore and follow the instructions to delete all restore points and switch it off. Malware can hide in here and re-install itself.
– Then right click on Avast and select Run As Admin. Let it run, if it wants to scan on reboot, let it.
– Repeat for Malware bytes
Reinstall the operating system.
Ask your parents…..