ok i have a acer aspire 5100 the processor is amd athlon 64x2 dual core processor 4400+ 2.30ghz the ram 2gb _i know this is slow im working on it

) i have a 500gb hard drive that is split with the main 228gb and the secondary 227gb now the main was almost completely full i only hard 20% free and the secondary is 10% i also hard a external hard drive hooked up the is 500gb with 20% free now i went and bought a 1tb western digital internal hard drive and freed up my main hard drive up to 50% which is 123gb free. now i used to have nod32 as my anti-virus and i thought this was the problem with everything going so slow with me possibly having a virus or something so after talking to xtreme i switched over to kis09 and it seems to me my computer was going slow so i went on here and asked whats the best defrag app and downloaded a portable diskeeper 09 which was the only thing i could get to work i didn't see any progress with the auto defrag so i did a manual and it only did about 30mins and said it was complete and my comp is still running really slow. im not sure whats going on, i used to use tune-up to clean my comp up but everyone says the multiple all in one apps suck so im not sure what to use to see if i have computer errors or what or a virus. i don't think it really can be the rams because its been going slow ever since i filled up my drive so much but i fixed that problem with getting a bigger hard drive. does anyone have any ideas what could possibly be wrong? thanks in advance