First of all - welcome to BC !
If I understand you correctly this aging computer is 'your main data store' and you are properly concerned with its reliability. I am sorry, it is an old song and I am going to sing it once again.
You are a business and presumably your data is important to you. You should have three copies of it. One accessible to the sytems in use; one backup of some sort in the office or whatever type of premise you use; and the third should be off-site to protect against the risk of fire, flood and Act of God.
The first is obviously on the hard drives in the computers in the network..
The second could be a NAS or similar system on the premises but NOT connected to the network except when doing backups.The reason for it not being connected except when actively backing up or restoring data is to protect you against threats such as ransomware. If your local backup system is permanently connected to the network and you suffer such an attack it too will go down.
The third copy should be off-site. It could be a remote NAS type solution or a cloud solution but definitely not physically on your premises, and also only connected when actively being used. The example I have referred to several times is that of a fairly large haulage company I used to work for - 80 odd tractors and about 200 trailers. They suffered a disastrous fire one night which totally destroyed their main office and their central warehouse. They were back up and running inside 12 hours, the time it took them to organise temporary office accomodation and to equip it with the necessary office equipments. They were able to do this because they had an effective system of off-site backups.
This is an area where you need expert advice and it is almost certainly worth paying somebody for this advice. After all, the future existence of your business and your jobs are otherwise at risk. And good current backups are the most effective defence against threats like ransomware.