Windows 7 hangs randomly after some period of inactivity

Whenever I want to eliminate hardware problems, I use a trusty Ubuntu LINUX LiveCD.  Download and boot it.  This does NOT install an O/S on your HDD, and it will work with vast majority of RAID controllers.    You then log in, ( it gives you a read/write filesystem based on how much RAM you have in the system).

Then after you log on, run some disk tests.  I just set up a script to perpetually read from all disk drives and throw it in the bitbucket.  

i.e.  dd if=/dev/sda of=/dev/null bs=64k &

(Substitute /dev/sda if this is not the appropriate name for your HDD.  Look at the logs that show up as it boots to see what the actual device name is)

There are also some diagnostics built into the disk for testing other things

Let it run all night.   If, when you come back in the morning you see it still running disk I/O and there are no errors, then you know problem has to do with windows, and not the hardware.   If you see a POST screen or the logon screen for Ubuntu, then you know the box crashed overnight and hardware is to blame.

Even if you have never touched a LINUX/UNIX system, it is still relatively painless.  Anybody who has enough common sense to know what expertsexchange is in the first place and who can make hardware changes such as you should have no problems figuring out how to run the diags.  

hello there.  excellent idea.  I will leave the disk  check running through the night and  rule out hardware as suggested.      I  will first  remove the SATA drive  and see if that stops the freezing.  I will revert after the tests.

Also run dmsg and look at /var/log/messages even if system stays up.  Something could still be throwing out error messages and LINUX is just more tolerant of them.  But the good news is that if it does stay online, and there are error messages, then you have confirmation on exactly what the hardware problem is.

Ann makes good point, but personally I would just start with the disk because it has higher probability of root cause.  RAM fails, but I put my money on a mechanical device rather than a failure on a molecular scale to hold a charge.

dlethe root cause analysis is probably correct, however how do you distinguish between a faulty disk and faulty memory? Answer is that you can't in general. So check memory first (or more the disk to a new machine and check it there).

Faulty memory will crash the system immediately, and it will not log anything.  Faulty disk will log an I/O error and since system is booted in RAM and errrolog is in ram, you will have 100% confidence if you get a disk error.  It would be different if the O/S wasn't running in RAM

I've seen one flaky bit in 4GB allow the system to work quite well most of the time.

The only observable behavior were occasional unexpected 'phase of the moon' errors that were never repeatable and seemed like disk corruption (and probably were). Swapping the hard drive and reinstalling the OS worked for a while, but the cumulative effect of bit flips eventually killed the new install.

The basic problem is that if the system is locking up, it's probably not going to behave as you expect.

Now obviously, if you boot Ubuntu and it reports a SMART error, then good for you. But I don't see how a disk read error will lead to a hung system. And so it makes sense to me to start from the basics, and work up.

Windows 7 has a built in memory diagnostic.  Run MdSched.exe and it will do a thorough investigation of the memory and tell you if there is a problem or not.

I had a memory issue with one stick.  Even MDSCHED would hang, but that was good.  I found that if I removed one stick I could get a full complete test and verify one stick was totally good.  I removed that one and put the other in and got the same hang on the test.  So I was able to determine which one was bad.

hello  experts ,  thanks for all your help.   After  a couple of days of  various tests,  I  was able to find the problem to be my broadband modem.  here is what i did.

I first of all removed the SATA dvd writer which was the only new hard ware I installed.    I then ran the machine in windows  again  and after  about 45 mins same problem  ,     I then   ran a disk check   and while doing that I took my broadband modem  and plugged into my laptop  so I could continue working.   my laptop then hang  after a period   too.    
 I did both memory and   disk checks on both computers  and they were fine.  Both computers dont freeze up   when   unplugged from the broad band modem .

I then  spoke to the ISP  who confirmed they had been having some trouble.  Next I had a look at the modem  settings  and  turned  on modem error control  and voila  !  working.  

Now,  I am not sure if modem error control  was the issue  or the isp  had something to do with it?

Ok for the points,   Dlethe  sent me on the right path so gets  the majority of the points,  Ann  gets an assist.    Mark  gets a  mention.   Hope its fair guys?  Thx

The  various tips led me to find a previously unconsidered  hardware that was causing the problem

So it was one of those unexpected behaviors after all.

I would be interested in knowing the cable modem model and the ISP explanation of the cause of the failure. It's disappointing to hear that faulty external hardware could freeze your system, but it also means that it could freeze anyone else too.

Forwarned...

what is make/model of the modem?  it would be great if you posted a followup that has all the keywords of the modem, and a sentence that it locks up your system. Then other people who have same modem can get a search hit on a single post that confirms it is (was) a known bug at the time you made the post.