Take the machine back (just in case it is a hardware problem, which seems unlikely; Sony makes good kit)
Get a new one.
Reformat the disk.
Install Windows.
Install one and only one anti-virus package, making sure that it is certified to run on Windows8.
And yes, the 'holding back a virus' theory doesn't hold water.
I suspect the problem is crapware. You've got a new operating system and I doubt that anyone has had time to properly test all the combinations of junk that OEMs like to force on you these days.
