Dell system performance is very slow

Hello,
I am using one Dell system whose processor speed is 3.2GHZ and the Ram is 512 MB. My question is that my system is working too slowly and I have done all things like defragmentation, disk cleanup, deleted temporary internet files, deleted files in Temp and prefetched folder, but it is still working very slowly. Is there any other method to increase my System Speed?
Thanks!
