Hello Gregf528

Welcome to PCHF
I am thinking that the problem may be related to your modem. If you are losing internet connectivity but maintaining a network connection with your router, then I would have to think your modem is at fault here.
The fact that it works for 30 minutes then stops tells me two things. Your internet connection settings in Windows are correct and your router settings are correct because you were surfing the internet at some point. And since you didn't make a note that you lose connectivity with your router, I will assume that your computer stays connected to your router, but you just lose the ability to surf webpages.
So I would say the problem is the modem may be defective, or maybe the internet port on your router is defective...but then I would think you wouldn't ever get internet working. This is all of course assuming this is a hardware related issue.
You could also follow my prework link and post the results in the Hijackthis! Logs forum to see if maybe malicious software is the culprit.
Hope any of this info helps you!
