High CPU Usage 100% in 32 bit Vista Home Basic

[MonikaDeodhar]

I have Dell Inspiron 32-bit Vista Home Basic for past 2 years and now the CPU Usage goes to 100% when viewing a video offline/online. I dont hear any fan sound and I am all the time on power plug. Lately, since 3 months I have been trying one or other options to solve the problem but now after just 5 mins of watching video, the CPU shows 100% usage in task manager and there is no single process that consumes it. Mostly, it will be iexplore.exe and other times it will be audiodg.exe, System (NT kernel), atm.exe (advanced task manager), Task manager etc...

My laptop details are:
Dell Inspiron 6400
Windows Vista™ Home Basic (6.0, Build 6002) Service Pack 2 (6002.lh_sp2rtm.090410-1830)
Intel(R) Core(TM) Duo CPU T2350 @ 1.86GHz (2 CPUs), ~1.9GHz
2046MB RAM

Display : ATI Mobility Radeon X1400
Display Memory: 894 MB Dedicated Memory: 127 MB Shared Memory: 767 MB Current Mode: 1024 x 768 (32 bit) (60Hz)
Monitor: Generic PnP Monitor Driver Name: atiumdag.dll,atiumdva.dat,atitmmxx.dll Driver Version: 7.14.0010.0489

Audio SigmaTel High Definition Audio CODEC
Driver Name: stwrt.sys Driver Version: 6.10.5614.0000 (English)

I have checked driver for updates thru Device Manager and they are uptodate

I have restored system to factory setting, windows update is done, drivers are up-to-date (as per device manager), no programs are there. Ran the test with Clean boot without any additional services load. Disabled even Norton AntiVirus and ran performance and reliability monitor to get Report of system performance... In report too, it shows CPU Busy 100% Investigate top process. I am not sure where to find those top processes in report and also the Processes in 2 reports ran for diff time frames are different.

I did the Process Explorer thing and these are my observations..

Firstly, I cleaned the back of laptop with a brush to remove dust.

With Clean boot and Norton Security off and with modem plugged off and then on

1) First time video (www.naruto.viz.com) went fine but with CPU avg usage as 25% with Procexp between 1-3 and System Idle between 70-75%. that was good..

2) After ending of first video, again started the same one but this time disaster. CPU avg usage as 71%, IE 62%. but then procexp went up to 30% and CPU usage was 100%

3) With readyboost, again started the same one . CPU avg usage as 71%, IE 62%. but then audiodg went up to 30% and CPU usage was 100%.

4) With readyboost, again started the same one. CPU went to 100% with IE as 40%, audiog as 30% Procexp as 25%.
(All above are approx figures. I have not given decimal values)

In all the above cases, Max CPU Cycles were used by System Idle Process.

MY WEI is 3.7 (score of Display)

Thanx