to make sure that the RAM you purchased was suitable for your motherboard?
Adding extra RAM is a favourite - and usually effective - way of boosting performance, but don't forget that the way computers handle data is a little like cities handling traffic. You can build a nice wide motorway into the city centre, but if the side roads can't handle the sudden increase in traffic flow you might as well not have bothered.
The critical components - the ones where bottlenecks can occur are a)the central processor b)the graphics processor and c) the hard drive. If any one - or a combination of these - isn't up to the job the performance of the whole machine can suffer. The unpalatable fact of life in computing is that a five-year-old machine may be reaching the point where money spent on upgrading it might be better spent going towards the cost of a new, much faster computer.
Check that the RAM is compatible first. If it is, make sure that your hard drive is defragmented, and that your anti-virus software is fully up to date - viruses can affect the performance of an otherwise healthy machine.