I think an important thing to remember here, and sorry if I’m making the wrong assumption, is that Oredigger77’s technical expertise is limited. In many cases it might be much safer to have files stored by a company who provides cloud service than to be stored locally by somebody who is in over their head. It also sounds like budget is a limitation, so making do with what is available may be much preferable to spending money to do it “right”.
A 7 year old gaming system is probably plenty powerful to be a small office server. I would strip out the fancy graphics card, just to save on electricity costs. Otherwise, as long as it has space to hold several hard drives, you should be fine.
I think these are the absolute minimum requirements:
[li]A sane backup plan[/li][LIST]
[li]The data should live in a minimum of two places (the active server and a backup)[/li][li]The data should live offsite[/li][/ul]
[li]Several drives to form a RAID (so failure of a single drive does not destroy everything)[/li][li]8GB of RAM (more is always better)[/li][li]an uninterruptible power supply (UPS) to plug the thing into[/li][li]gigabit wired ethernet, even if the clients are all on wireless[/li][li]A sane backup plan[/li][li]Also, a sane backup plan[/li][/LIST]
That is all assuming you are storing spreadsheets, word processing documents, and the like. Things of a relatively small size. If you will be storing multi-gigabyte files, then the size of the server will have to be scaled up appropriately.
If your requirements are only office documents, and such, then something like Microsoft or Google’s cloud service might be the best option. Using a cloud service doesn’t change the requirement for backups, regardless of what the service promises. Failure of the local internet or the cloud service will impact your business operations. The important questions are: Is it more likely your local server goes down, or the cloud service goes down; how much money is it worth it to spend to buy more reliability; do you have more time or money—should you be spending hours that could be billable managing your own environment? Many of the local applications for the cloud services allow an offline mode, so you can continue to work if the internet is done. Again, this is a good option for small documents, but not massive files.
You might look into things such as FreeNAS, which is designed to convert a PC into a purpose built file server. Any server oriented Linux distribution will be able to do what you want (Ubuntu LTS, CentOS, Debian stable, etc.) None of them will be simple for somebody not otherwise experienced with such things. They all will be pretty easy for somebody who is experienced with such things.
If you decide to buy a proper small server, you might be able to find some cheap Poweredge T (tower) series servers in Dell’s outlet store.
A Synology, Drobo, Qnap, or other dedicated NAS appliance might also be a good option.