Did you already DISABLE FLASH HARDWARE ACCELLERATION (Google that if you don't know what I mean or how to do it)?
I built a system for my wife in January with parts that were given to me by a very generous friend who had extras. It's a bit of a random assortment and I added some myself. This system has worked fine until we moved to a new place. In the new place we were forced to add a wireless card for internet because of the layout. Since adding that card the system has experienced repeating, random reboots. I say random, but they only seem to occur when watching youtube or another online streaming video site. There is no graceful shutdown, just a straight out reboot. We checked the temp with a monitor and the CPU was getting pretty hot so we added a nice aftermarket heat sink that keeps the CPU temp at about 45 under load. The system gets cleaned pretty regularly, it isn't dust.
Problem still happened. Checked the wall outlet with a multimeter, steady voltage. Looked into the power supply, and a handy online wattage calculator told me with all the parts we have my wattage could, under heavy load, be inadequate. One beefy, expensive power supply later I find myself still experiencing this problem. I'm really hesitant to throw more money into this at this point, but my wife needs a computer that works.
My next thoughts were to update everything (BIOS, drivers, etc) and if that didn't work go the route of rooting out a trojan/virus causing problems by booting to safe mode and running a hitman scan. I couldn't imagine how a virus could get on her system since we don't use torrent sites, any *ahem* unmentionable sites, and we've had Kaspersky running from the get go. I also keep the drivers and such pretty well updated (I could have missed a REALLY important one I guess) so I don't really have a lot of confidence in that course solving it.
Anyone have any ideas that might point me to a more productive line of reasoning? This problem is getting frustrating. Below is what I have for the system. (I am suspicious of the odd motherboard, it seems to have been made in 2002 and might not be best suited to work with newer stuff)
-Hybrid CFX motherboard by MSI
-AMD FX 8150 (8 core)
-HIS Radeon HD 7850
-2 Corsair 4GB DDR3 1333 sticks
-Termaltake Smart 850W PSU
-Either a simple TPLink or Linksys PCI wireless card, not sure have to double check that
-Windows 8 Home Edition