IS it possible to download a unique pgn file with all my previous games played on chess.com. When I try the software bugs.

How can I fixe this?

Do you mean one big PGN file with ALL your games? both live and regular online?

to get your archive for live games, click PLAY, then LIVE CHESS, but before actually going to the game board, you should see recent games, and above that there should be a link that says "view games archive". That should be it, just select all and download

For online games just click PLAY then ONLINE, and same thing, click games archive and download the PGN file

When you say "the software bugs", what exactly do you mean? What is it doing that you didn't expect? Or what is it not doing that you did expect? It will be hard to help you with out more specific information.