My computer lags every half a minute. god knows what the problem is

My computer lags even though i've changed my graphics card.. SO BUGGING!!!?
I have a 2GB ram, 350 GB SATA hard disk, 9800GT card, m2nmx motherboard, AMD Athlon 64 x2 dual core processor 5200+,.

Earlier i used to have a 8600GT card, lots of games life PES 2010, NBA 2k10 n others started lagging periodically i.e works fine for a while then lags for about 5-10 seconds then works fine and continues to lag again n again.. Earlier this never happened...it started gradually. so i thought that this was because of the graphic card and finally changed it. but this problem continues. i can't figure out what the problem is..

 

Open up "Task Manager" and check the amount of processes running. If you've got more than 40 then you should remove some processes.

Click Start, and in Run type in: msconfig
Go to the Startup Tab and uncheck all but necessary programs to start up such as your Antivirus, drivers, etc...