problem. {unrecognized shell commands}

i dont know why but my new computer does not want to accept dos commands i always get the same error.

'whatever command' is not recognized as an internal or external command, operable program or batch file.

anyone know why this is happening and how to fix it.
I use windows xp media center edition.

...What commands are you trying to use specifically. "Whatever command" is not a dos / command prompt command.

it does not recognize anything
examples : help, net, ipconfig, netview, regedit, everthin!!

Long shot, but check that the PATH environment variable is set and includes things like the Windows directory, \Windows\System etc.