System freezes on HP NC6400 when browsing the web at random

Hi, I have a problem I cannot solve with drivers or software, I have serviced two HP's that have the same recurrent problem, basically, they randomly freeze with no response from any part of the OS (Vista business SP2 32bit) when browsing the web, and later on just randomly with the older NC6000. The first one that exhibited the problem was an old NC6000, everything works fine on it, just this random total freeze that requires a hard shut down to fix after between 20 minutes and an hour of usage.

Now it's successor, the NC6400 has the same problem, in fact I am typing this post on it now, with no problems, just that without warning, without any kind of similar actions before, it just freezes with the screen showing what I was doing at the moment in time.

All of the drivers are updated to the latest versions on both these machines, and the hardware (DVD drive, quick launch, wireless, bluetooth, ambient light sensor etc.) seems to have no problems.

Some possible solutions or remedies would be greatly appreciated,

Many thanks, Dann

You can run a virus scan with Malware bytes: Malwarebytes

Try doing a system restore to a point before your problem occured.

Performance tweaks:
http://www.vistax64.com/tutorials/81176-speed-up-performance-vista.html

run chkdsk to see if you have any hdd problems: How to perform disk error checking in Windows XP

run memtest86 to see if you have memory problems: Memtest86 - Free software downloads and software reviews - CNET Download.com

Go into safe mode and open the elevated command prompt and type in: sfc /scannow
to check for file integrity errors.

*Do all of the above in safe mode (repeatedly pressing f8 after post).