Expired? O_o I didn't think that was possible. Mine is still open, and doesn't say it's ever going to expire. Did you maybe fill it up?
Either way, you can still download files from MEGA (We're talking Mega.NZ, right?), if you open the links in a Private Browsing window or Incognito window. Just make sure to NOT choose the "Download with Mega", and just the straight download option.