As a last resort to my ongoing problems I ran the recovery console from XP Pro setup and told it repair my MBR. It came up with a warning that something was wrong with the MBR and a repair could cause loss of data etc, I fixed it anyways and all seems fine.

What I would like to know is that could a damaged MBR cause a PC to boot OK, run fine for anything from 10 minutes to several hours, and then crash and not boot? The problem I had was the monitor would appear to go into standby mode and the PC would just freeze with the HDD light on constant. Trying to restart would do nothing for many hours, no bios beep like normal or anything, and the monitor would stay in standby with just the HDD light on solid.

I have eliminated the vid card and RAM as issues now, all the shit attached like printer, scanner and any USB devices have been eliminated too, I guess it just leaves HDD, CPU and mobo, possibly the PSU I don't know. I have a SMART monitor running, but this has shown no issues right up to the destruction, but I am still running it. Also have a temp, fan speed and voltage monitor for my mobo/CPU and this has shown no issues either. Any more suggestions for tests and the like would be appreciated.

you have been checking your error log right? My Computer>Manage>System Tools>Application or System.

I'm surprised by how many people forget to look at something that logs most of the stuff your pc does

Oh faulty MBR can screw up as you describe, when it is trying to access a disk space beyond where the fault is, it will just screw up and be unable to process data. Windows should log any disk errors in the error log

Well it has been running fine since the MBR repair. The logs dont make much sense to me, but nothing stands out to me, just messages about

Event Type: Warning
Event Source: Userenv
Event Category: None
Event ID: 1517
Date: 18/05/2004
Time: 19:55:53
User: NT AUTHORITY\SYSTEM
Computer: MEANMACHINE
Description:
Windows saved user MEANMACHINE\TaKYoN registry while an application or service was still using the registry during log off. The memory used by the user's registry has not been freed. The registry will be unloaded when it is no longer in use.

This is often caused by services running as a user account, try configuring the services to run in either the LocalService or NetworkService account.

and

Event Type: Error
Event Source: Service Control Manager
Event Category: None
Event ID: 7001
Date: 20/05/2004
Time: 13:24:52
User: N/A
Computer: MEANMACHINE
Description:
The Internet Connection Firewall (ICF) / Internet Connection Sharing (ICS) service depends on the Application Layer Gateway Service service which failed to start because of the following error:
The service cannot be started, either because it is disabled or because it has no enabled devices associated with it.