If you are worried enough about a professional hacker, then you should have serious firewall hardware which will record all traffic.
Do you practice good computer security? Passwords greater than 8 characters with upper, lower, number and special chars? Do you change your passwords every 90 days? Do you reuse passwords anywhere?
If the standard AV / malware scanners show nothing then you probably haven't been hacked. But if you are concerned, use DBAN to wipe the disk and start over.