I used some program to locate my key( i could easily do that searching in the registery too), wrote it down and used it in the fresh win 10 installation. it shows up as activated now. :beer: i guess doing a clean install is the best option. the other time i tried win 10 it was just after upgrading from win 7 with heavy loaded hard drives and programs. something went wrong there and it kept freezing on boot. now it's all good!
as for antivirus, i sticked with eset Smart security 9 for now. on win 7 i had eset 4 and i was very satisfied.
so all in all, win 10 seems to be pretty stable now. then again i have a very high end rig now, guess it doesnt make a difference as long as you wipe everything and install win 10 fresh you should be ok.