networking - No internet access on Windows 7

I have a strange problem with Windows 7. It all started couple of days ago. On my Dell XPS laptop I have two network interfaces, one LAN one WLAN. When I power up my computer I have a small yellow triangle on network icon that says no internet access for my LAN connection. I have an IP address from my DHCP. Ping does not work and tracert outputs this:

Tracing route to superuser.com [69.59.196.219]
over a maximum of 30 hops:

  1  XPS [192.168.1.124]  reports: Destination host unreachable.

Trace complete.

The first time this happened I googled a bit found this tip:

netsh int ip reset

I ran it, rebooted, and it worked. The first time. Next day it didnt work. I ran it a few times, fiddled a bit with networks and it worked. Next day, nothing worked and thats why I'm writing here - cause I'm out of ideas.

And another thing, if I disconnect LAN cable and power on WLAN everything works fine. I wonder for how long.

What should I do? It seems the only solution is to reinstall Windows 7 from scratch but if I'll have to do that every 30 days (yes, I installed it 30 days ago) - screw Windows 7, I'm going back to XP. I need my network to work!

Answer

Windows 7, same as Vista, supports only one internet connection, and in addition has the annoying habit of always preferring wired connections over non-wired, on the supposition that they are faster (have better metric).

See this article for a Vista solution with many screenshots :
"Windows Vista Multiple Networks: Wireless To Public WIFI and Wired To Private LAN".

The basic solution is to use the command:

route delete 0.0.0.0 IF 11

where the IF 11 refers to Inteface List # 11 (which is displayed by route print command output, in the Interface List section). Replace this by the number in your case.