Is there a way to tell if someone has hacked my computer?

You can't unless you have a tracer that records what was accessing your computer. Computer maybe getting harder to hack because almost every router has a NAT for better protection. NAT give a artificial IP while hiding your real IP and giving you internet connnection.

Hackers will come and go. If they don't have your IP address or they can't go into certains port than they can't hack it. It getting harder and harder, while hacker will try a different approach by leaning toward using trojans and keyloggers.

You can use task manager to see what processes are running. (press crtl-alt-del and select task manager. Or you can right click on the task bar at the bottom of the windows screen and select task manager. Select the processes tab and select show processes from all users. Processes that are running will take CPU time. You should see this number change as programs are running. "system idle process" is time that the processor is doing nothing.

With a antivirus beacuse most hackers take over computers using a virus and having the virus execute commands. Use one of the billions of antivirus's to get rid of it.

If it runs by itself doing things, that is a tip off, if it runs at night, that too ! If you see files that look strange ! If it gets busy and stays busy by itself !

i'm sure there is a way but to be safe run a virus scan once a week

See if there is anything unusual or wrong about it.