If your Windows XP computer can't communicate on the network, try opening a command prompt and typing ipconfig. If your IP address displays as 169.254.x.y then your computer probably rebooted recently but couldn't contact a DHCP server to lease an address, and as a result your computer auto-assigned itself an IP address using Automatic IP Address Allocation (APIPA). Try typing ipconfig /release followed by ipconfig /renew to release the APIPA address and lease a new address from the DHCP server. If you still get an APIPA address after this, then either you have a network connectivity problem between your computer and the DHCP server, or the DHCP server is down.
Mitch Tulloch is President of MTIT Enterprises, an IT content development company based in Winnipeg, Canada. Prior to starting his own company in 1998, Mitch worked as a Microsoft Certified Trainer (MCT) for Productivity Point International. Mitch is a widely recognized expert on Windows administration, networking and security and has written 14 books and over a hundred articles on various topics. He has been repeatedly awarded Most Valuable Professional (MVP) status by Microsoft for his outstanding contributions in supporting users who deploy Microsoft platforms, products and solutions. Mitch is also a professor at Jones International University (JIU) where he teaches graduate-level courses in Information Security Management (ISM) for their Masters of Business Administration (MBA) program. For more information see http://www.mtit.com.