well, that sounds like remote desktop/equivalent being used. most likely due to someone managing to sneak a trojan that set it up on your computer.
As noted above, change password now, do a virus scan/malware scan, clean stuff up, change password again (since 1st change could be compromized with keyloggers but with any luck, would give you more time to do the scans)
Also since it is remote, booting to safe mode without networking (or unplugging network/wifi) would cause it to stop while doing the scans.
Click start in the bottom right and right click computer and go to properties, then on your screen (probably top left) click remote settings and uncheck Allow remote assistance to your computer. As said by litte_me run a virus scan and change pass, after the scan change password again