Signs That Your PC is Infected with Viruses
1) Unusual Network Traffic
Even after closing your browser, some applications use internet and download or upload some files. Make sure what you are downloading or uploading. Some viruses will also download along with the downloaded files which can harm your system. If you are using wifi, make sure the wifi is properly secured.
2) Internet Connection
If your Internet Connection suddenly stops or slows down suddenly, Some virus is present in your system. Make sure that your internet connection is perfect.
3) Computer will not boot
If your Computer suddenly stops booting, the reason is some virus has modified the O.S files and crashed your system. The only solution is repairing your system with recovery disc.
4) Slow down of Computer
Some viruses are designed specifically to increase your CPU's usage level to 100%. If on running the Task Manager, you find that your CPU's usage is constantly at 100% level, a malware might be the cause.
5) Programs will start automatically
Some viruses and adware automatically start strange programs on your computer in order to show unwanted advertisements. It means your PC is infected with virus.
6) Unusual File Extensions
Some viruses change .exe or other file associations which prevents these files from opening. Some viruses also do this to automatically start themselves when a file of a particular type is started.
7) Programs will not start or crash suddenly
If some system programs like the task manager or registry editor have suddenly stopped working or crash randomly without any visible reason, it is more than likely that your computer has got some form of worm that is attaching itself to various programs and thus, corrupting their code. A virus modifying registry entries to prevent these programs from running could also cause this.