If it is for the AV, just fire the AV up and when it installs it will ask for the registrations number.
A note, a lot of the "off the shelf" builds through third party retailers use "standard" PSU's. These have a very high failure rate and have been known to fry systems. I would open the case and take a look. If it has Corsair, Coolmaster, XFX, Thermaltake, EVGA you should be fine. If you can't find a brand or you see "standard" I would seriously think about getting it out of my system. Some of these have lasted a year or so then all of the sudden a GPU goes out or your system won't start or you smell something burnt. These may well be providing "un-even power" (ripples) which is very hard on components over the long haul and if they fail you don't connect it to the PSU.
You may also have lower end RAM. At least download Memtest, it is free software that tests RAM for bad sectors. Just a few bad sectors can make you machine do all sorts of weird things.
The membership will never suggest an off the shelf build. People who check her ahead of time we ask what their max budget is and what the system is for. Then the membership chimes in with suggestions for a solid build and in some cases save people cash.
Remember valor, honor, independence, family & clan; I do whenever I hear the ceol mor, the "great music" of the Highland bagpipe. I swear upon the holy iron of my dirk that I will not forget.