If there're entries in Device Manager with ! or ?, they need the correct drivers. Have you booted to Safe Mode and checked for viruses and other malware? Have you run SFC to check for corrupt system files? Open an administrator command prompt and run SFC if the above doesn't help. Click START, then type CMD in the search box, right-click CMD.EXE and click Run as administrator. Then from the command prompt type sfc /scannow.
I've run into an unusual issue where I can access the Internet normally, as long as I don't shut my computer down. Without fail for weeks now, every time I start my computer back up it can't connect to the Internet through the LAN. The wireless appears to function regardless for my three roommates, but the only way I can regain access to the Internet is by restarting the wireless router and cable modem. I've tried changing the DNS, as well as a variety of more traditional troubleshooting methods on my computer, with no success. The problem, as near as I can estimate, started when I purchased a Belkin Belkin N450 wireless router to set up a WLAN in my new apartment, but I'm unsure why my computer is the only one affected.
I'm running a Dell XPS 210, running 32-bit Vista with all the Service Packs and downloads to date. I'm using a Ralink 802.11n Wireless PCI Express Card LAN Adapter to connect to the network. Apologies if I've missed anything.