|Hmm older system.|
Right click on My Computer and choose Properties and see what it says there for memory.
Go to Device Manager and see what it shows for installed memory.
Check in BIOS to see if there is a certain amount or percentage of memory reserved for integrated graphics. If you use integrated graphics, you may be able to adjust this, especially if it is by percentage and you recently increased the amount of memory. If you use a PCIe graphics card, it has dedicated memory so there does not need to be any reserved for graphics use (consider adding one if you do not currently have one).
Do not spend too much on that system since it is quite old and putting away money towards a more modern machine may be a better path for you.
You have to be a little bit crazy to keep you from going insane.