Having connection problems with windows 7 on my iMac. Any suggestions?

Okay, so i got a new modem from my ISP after upgrading to faster internet.

When i log into Windows 7 64bit, my internet will work for about 30 minutes, then goes out. It doesn't do this on OS X.

Here's the dialogue that comes up after troubleshooting with windows.

"Local Area Connection" doesn't have a valid IP configuration.

The troubleshooter fixes it, but after i restart the computer, it does the same thing over and over again. Its getting really frustrating!

Could anyone help me with this?