If no improvement with a dedicated video card, then the problem is elsewhere.
Several other factors can be a cause for poor performance.. especially a PSU that has little or no reserve! Those "off-the-shelf" packages rarely have robust PSU types.. only adequate for how the system was built.
Best to list the full details of the system..
CPU ID tag
These factors will help with better suggestions for a cure. AMD does not have an "easy" reference chart like Intel does. But with either, you need the specific stepping number or core ID to get the exact specs. Some processors rely on a 200 Mhz FSB base, fine with 400 Mhz memory speed. But if the CPU requires a higher FSB base, then memory must also be compatible to that speed.. or performance will suffer.
And with some AMD products, the socket may be identical in appearance.. yet be wired differently, and not accept all CPU models. Then too, older motherboard models may not be capable of true 64-bit operation, even with a BIOS update.
F@H.. to solve mankind's maladies.. in our lifetimes!