After update internet works for only for 5 min?!?

I updated my pc that hadnt been updated in a while/months/years now I can only go on the internet for 5 min before it quits. I have no router, a cable modem that works on my laptop, but my desktop wont stay on for more than 5 min until I restart it and then 5 min again. The funny thing is I can play poker if I load it while the internet is working and it will continue to streamline? I've tried Google Chrome and IE and both are the same. I used Malware and Advanced System Care to clean up and no results. I'm hoping someone here will help. Thanks in advance

 

Windows xp recently updated. Avg anti virus, ie version 8, no wifi Ethernet or Wan. Firewall is on. I'll try safe mode and let u know if the Internet stops after 5 min.

 

Yeah I just tried to surf the internet while in safe mode, no luck. It sometimes wont even go on the internet after restart. but like I say if it does only for 5 min but will let me streamline a poker game.