Freezing PC when browsing, needs restart to "fix."

Hello ladies and gents..

I have an Acer Veriton PC, running W7 Pro, and am having problems with it freezing up on a regular basis when online.

This happens in FF, Safari and IE, (3 users always use their own browser choice.)
Restarting solves the problem every time.

It can freeze just browsing, with single or multiple windows or tabs open, social sites, games and even when emailing. The 'puter fails to respond to any command, e.g. I can't even close Windows.

It also sometimes will freeze trying to update, for example SAS or Malwarebytes, also "fixed" by restarting.

I get my connection through BT, (UK). But I don't think that's my problem.

Thanks.