If someone was messing with the computer through VPN and he does not know for sure whether that was his friend or not, did not sound good.
To be honest, i would never let anyone mess with my computer through something that i cannot 100% monitor what they are doing.
The person that set the VPN up may have not set it up securely (Possible, not necessarily the case).
If it were me and a friend sends back "n..:=) m a friend..." after me letting them access my PC remotely and weird behavior ensueing. I would nuke the machine immediately, re-write the router's firmware with a clean legitimate copy.
I would not let anyone mess with my pc, even if I monitored him.

Tressco if I were you, I would:
1. scan with various AVs the boot sectors of the hard disks.
2. format C:\ and installed a fresh, clean windows
3. would never allowed again anyone and I mean anyone to have controll over my pc; especially from distance!
p.s. when I help my friends I let them do the necessary tasks and the only thing I do is guide them. This way they will remember those things and probably the next time they will be able to resolve a similar problem by themselves.
