Open Start -> Settings -> Control Panel -> Device Manager and see if the network card driver for your ethernet or wireless card is installed. If it is not installed, you may find some ethernet adapters with a "?" icon on them. If this is the case, you need to find the driver for it, or download it from a computer that has internet (can probably get it from Dell.com (or possibly it is on one of your recovery CDs) if it is built in and you are on a Dell Computer). If it is from an add-on card, get it from that manufacturer via their CD or website. Once you have the driver, expand it to a directory on your hard disk, right click on the adapter with the "?" icon, and choose "update driver". Select the folder in which you extracted it to. There are also some drivers that use their own installers instead of the "Update Driver" method in which when you copy or extract the drivers, look for a file named setup.exe or Install.exe (other names are also possible) in the directory you installed the drivers to and run it. Once you install the driver, this should allow IPConfig to work again.
If the driver was in fact installed, open the "Network Connections" control panel and make sure that the adapter you are trying to use is enabled (not grayed out). If it is disabled, then right click it and enable it.
The third possible cause of IPConfig not working, is that the adapter you are trying to use does not have the TCP/IP protocol installed on it. To do this, go into the "Network Connections" Control panel, right click the adapter your are trying to use and click on "properties". Make sure the TCP/IP protocol is installed on it, and if it is not, add it.