Check network configuration:
ipconfig /all
Release (reset) and renew your DHCP IP address:
ipconfig /release
ipconfig /renew
Flush the DNS tables. If DNS is screwing up, try this first - it's often needed when you'd least expect it!
ipconfig /flushdns
Change file attributes. Type attrib /? for a list of switches:
attrib
Check which ports are open.
netstat -a