error unpack any tgz arhive

[gispita]

hellow , i have a lot of arhive and any think i try to unpack its not workng the error its all the time the same ,


gzip: stdin: not in gzip format
tar: Child returned status 1
tar: Error is not recoverable: exiting now


i have try with new athive from internet i have try with arhive from my old cd all the time the same error , i try with a lot of unpack command and nothig happen

any one can help me to reinstall the tar file or what can i do ?
Thanks in advance !