Computer slow :cpu usage ultra low 5% ram usage: 50%

Brothers i have a Intel Pentium D 805 @2.66 ghz and 512×2 gb of ram, Intel Original D945GNT motherboard and a 160gb sata hard drive a few days ago it was working fineeeee BUT from a few days its dead like it took me 63 minutes to copy 6 gb of data from my hard drive to a sata hard disk connected bia usb on 2.0 port
also wen i play games such as counterstrike 1.6 it lags lags lags lags for abt 20 minutes after which it gets stable BUT if i minimize and go back to game it starts laggiing and gets stable after 15 -20 minutes
i defragmented all the partiotions and all partitions have 3-9 gb of free disk space also if i m copying smthing i cant do anythign else not even play a song it just makes my comp dead like i tryind everything diskcheck,registry cleaner,defragmentaiton…..
but cant get this problem to flee I am running windows xp sp2 and an average 40 processes run of which 90% re of system
thnx in advance
PLZZ HELP
Answer #1
Could be 1 memory stick or motherboard faulty?
Change memory sticks for different and tries again.
Answer #2
what have you changed/added lately ?
is task manager showing any CPU usage while the lag is occurring ?
you scan for viruses or spyware ?
Answer #3
all clear no virusn no spyware no trojan no nothing no additions to hardware
Answer #4
no it doesnt show wen lag is occuring
Answer #5
Post your hijackthis log.
Answer #6
open pc clean cpufan from dust test cpufan maby death.