These are the greater possibilities that your system is infected by a virus:

slowing down of your input or it freezes
slowing down in loading of any thing from an application program to a website
strange display, messages, things that happen without your knowledge

if you are the only user of your system, and
- you cannot access a program
- you cannot open a folder
- you cannot make an input
- your webcam suddenly turns on without you activating it

If you have had other observations that brought you to a conclusion that your PC has a virus, please contribute them here to benefit everybody.

Your computer is infected.