I'm having an issue with my computer where it will work for between 20 minutes and several hours, and then without warning, it will stop receiving data from the network. the computer is running Windows XP x64, and is joined to an AD domain, where my user is a local admin on this PC, but not on the domain. My previous PC had the exact same problem, which is the main reason why I got this new one. I have tried the following troubleshooting steps:

Replace patch cable from wall jack to PC
Replace patch cable from patch panel to switch
Connected to a different wall jack and tried all of the above again.
Switched from DHCP to static IP

I have Visual Studio 2008 Professional installed, with SQL Server 2008 Express.

I have disabled the services for SQL Server, with no effect.

whether I am configured with static IP or DHCP, clicking 'Repair' on the network connection resolves the issue, but it occurs again eventually, but sometimes not for several hours, and other times as soon as 10 to 20 minutes.

I've run out of things to check, and I'm just about to go homicidal on this issue.

Please help.