detecting computer tampering

Can you tell if a computer has been dismantled and put back together by checking data on the computer? I have a Toshiba Satellite C665 and took it to a shop for virus removal and when I got it home noticed a screw missing from its place on the back panel. The shop has not informed me of any dismantling and when I check the event log (which I don't really understand) there appears to be over 24hrs of shut down period. I hope im just paranoid but I would just like to be sure.