how to make sure the pc is OK after heavy browsing

we had a guest who had to do lot of research and browsing for a whole day..

next day (yesterday), i saw that there was an automatic popup that was not controllable.. i tried to close it but could not.. also it did not seem like an ordinary regular window we are used too,..

i shut down the machine right away.. i booted it today to see if i will see the symtoms yet.. i do not see any..  i am not browsing.. just waiting to see if anything will happen..

i am typing this from another pc..

what tool would you recommend to make sure the pc is kosher and that nothing is hiding etc

thanks