Question : Problem: CPU Usage randomly spikes when watching videos

I thought I could ignore this, but tonight just reaffirmed that I have to fix this problem.  Within the last 1 or 2 weeks (can't pin down the exact date), my computer has been acting up with random lag spurts.  

Before I start, here are my specs:
Dell Inspiron 9400/e1705
1gb Ram
Nvidia GeForce 7800 GO
80 gb hard drive
Intel T2500 Duo Core 2.0 ghz processor (so 3.6ghz roughly)
Windows XP Home SP2

It all started when I tried playing Neverwinter Nights 2.  My computer is supposed to have passed not only all the minimum requirements, but also all the recommended ones too, yet the game ran horribly slow even on all the lowest settings.  I decided it was time I updated my drivers; maybe that would fix it.  I updated my BIOs as well as my video card driver and the performance might have been a little better, but it wasn't that noticeable.  I decided instead of dealing with that, to watch some videos instead.

At first, the lag started happening after about an hour or so of watching a video.  During the video, the sound would keep going for a bit, but the video would freeze.  Then the sound would get choppy as it continued to play, but the video remained stuck.  In fact, my entire computer was slowing down.  It took forever for anything to load.  I eventually loaded up the task manager to find the CPU Usage constantly fluctuating somewhere between 85-100%.  I went to the processes tab and noticed that like 6 of my background programs got a spike of 5-20% cpu usage.  The numbers kept fluctuating and seemed almost random except that the System process always took up the majority of the cpu usage.

I decided to start ending processes on my computer.  I started at 55 running processes and got it down to 50 when the lag started to dissipate.  It took about 5 minutes.  I went back to the video and not even 30 minutes later, it started happening again.  5 minutes later, and 5 processes less, the system started returning to normal.  Then it happened again 20 minutes later.  I then had only 40 processes.  10 minutes later it happens again.  I realized it can't be any specific process that's causing these problems because every time my computer starts lagging, ANY running processes get a huge spike in cpu usage, even if they barely do a thing.

Just a simple restart did not help.  I did a system restore back to the beginning of the week, but it didn't help.  I noticed that even when I was playing music or just idle, the lag attacks would still occur, sometimes lasting for 10 minutes.  I reinstalled my old video driver and thought that fixed it.  I was wrong.

Sure, the lag spurts now did not happen while I was idle or listening to music, but they still happened while I was watching videos.  Usually they would only last for 5 minutes or so and then go away.  I did a virus scan, spyware search, and a hijackthis log analyzer.  I ran some windows tune up utilities to try to tweak the registry and I disabled a bunch of startup programs, but it did nothing noticeable.  After exhausting all my options,I gave up.  It wasn't too horrible since reinstalling my old video driver since it usually went away after 5 minutes or so, but I didn't know what to do.

Well, just a couple hours ago, I came back from a friend's place where we plugged in my laptop to output to his big screen TV so we could watch a movie I had on my hard drive.  There were about 6 other people that I was just meeting for the first time watching with us.  The movie night was going great until... the lag spikes returned.  I was so embarrassed.  After more than 5 minutes of consistent lag, I had restart.  It happened 5 times during the span of the movie, 4 of which I had to restart.  I tried different media players, but it did not help.  Almost everyone left by the end.  I felt so bad.  I knew it was time I asked the experts for help.

As a side note, I think the occasional lag spurt while watching movies might have happened once or twice before I installed Neverwinter Nights 2, but they weren't as bad.

Any help would be great.

Answer : Problem: CPU Usage randomly spikes when watching videos

Very generally and disregarding anything that may already have been said about overtemps here, I'd like to point out 3 things:

Blockage of the air flow ==> check for and, if applicable, remove dust or other foreign matter that hampers airflow.

Fan not spinning as it should ==> check fan for bearing problems or anything else that may cause low fan speed (dust, as an example, or hairs)

Heatsink not in full contact with processor cooling surface ==> disassemble and reassemble, with new coating of thermal compound.
/RID