I assume from your message that you mean you can't print a document from your computer or send and receive faxes. Chances are, you'll have to reinstall the printer, just the same way as when you first bought it and hooked it up to your PC. Also, the operating system on your computer is going to make a difference. For example, if you originally hooked the printer up to a Windows XP computer and now you're hooking it up to a Windows Vista computer, you'll need to install different print drivers.
I don't know if you have the original manuals or disks that came with the printer. If not, a good place to start would be to download the manual from HP.com. That'll at least get you started:
It would be really helpful if you were to post what steps you took to connect your printer to your PC once you got the printer out of storage. Also, how long had it been in storage, are you hooking it up to the same PC or a different PC than before you put it in storage, and are you hooking it up to the PC differently now than before (printer cable vs. USB cable, for example)?