No error or problem was found with error reporting. The reliability and performance monitor shows that everything passed. It says no problems found on this computer.

On step 2: Disruptive shutdown (well that had to be on purpose)

On step 3: error for today:

1)Unable to initialize the security package Kerberos for server side authentication. The data field contains the error number.

2)Initialization failed because the driver device could not be created. Use the string "00241D154D3E" to identify the interface for which initialization failed. It represents the MAC address of the failed interface or the Globally Unique Interface Identifier (GUID) if NetBT was unable to map from GUID to MAC address. If neither the MAC address nor the GUID were available, the string represents a cluster device name.

3)Initialization failed because the driver device could not be created. Use the string "00241D154D3E" to identify the interface for which initialization failed. It represents the MAC address of the failed interface or the Globally Unique Interface Identifier (GUID) if NetBT was unable to map from GUID to MAC address. If neither the MAC address nor the GUID were available, the string represents a cluster device name.

4)The previous system shutdown at 09:17:06 AM on 21/06/2009 was unexpected.

5)The BDSelfPr service failed to start due to the following error:
The system cannot find the file specified.

6)A timeout (30000 milliseconds) was reached while waiting for a transaction response from the ShellHWDetection service.

The above errors are from the 3 boots today. Some of the above errors occur more than one so I would say some for each boot.

On step 4: there was hardly any problems in the history. The first one, is with ISCAb program compatibility. The rest are firefox and ie.

5)The BDSelfPr service failed to start due to the following error:
The system cannot find the file specified.

This indicates an issue with your BitDefender program. If you're still using it, I'd suggest a malware check and then an uninstall/reinstall of the program.

FWIW - it's my opinion that you shouldn't use fixit utilities, especially if they mess with the registry. Eventually the registry tools will hose the registry and the system will have issues because of it.

Once the BitDefender has been removed and reinstalled, see if the system still locks up on you. Please let us know the results.

I wouldn't go back to Norton 360 either. But if one of the BitDefender services isn't working, then your protection is lessened (and may not be working at all).

Download a new copy of BitDefender
Save/collect your registrations info
Uninstall BitDefender
Reboot
Reinstall BitDefender
Update BitDefender
Reregistry BitDefender (if neccesary)

There's gotta be something wrong - otherwise you wouldn't be getting Blue Screens.

FWIW - errors 2 and 3 refer to drivers - so there is a driver issue. It's my hope that the driver errors are from the BitDefender and will be fixed by the uninstall/reinstall.

Also FWIW - IMO the breakeven point for RAM in Vista (and Win7) is 4 gB. If you're never going to use more than 4gB, there's no point in using an x64 version of Windows. What RAM is lost to overhead in x86 (32 bit) versions is around the same as the extra overhead required to run x64 with the same 4 gB. Should you decide to upgrade to 6 or 8 gB - then x64 is worth the extra effort.

It's your system, you do with it what you want to do.
But I question it because BitDefender is broken according to Item 5 that you posted in Post #3.

The only other suggest that I'd have is to run Driver Verifier.
Read the following instructions carefully before starting it up.
Then post the resulting dump file here for us to have a look at.

Using Driver Verifier is an iffy proposition. Most times it'll crash and it'll tell you what the driver is. But sometimes it'll crash and won't tell you the driver. Other times it'll crash before you can log in to Windows. If you can't get to Safe Mode, then you'll have to resort to offline editing of the registry to disable Driver Verifier.

So, I'd suggest that you first backup your stuff and then make sure you've got access to another computer so you can contact us if problems arise. Then make a System Restore point (so you can restore the system using the Vista Startup Repair feature).

Then, here's the procedure:
- Go to Start and type in "verifier" (without the quotes) and press Enter

- Select "Create custom settings (for code developers)" and click "Next"

- Select "Select individual settings from a full list" and click "Next"

- Select everything EXCEPT FOR "Low Resource Simulation" and click "Next"

- Select "Automatically select unsigned drivers" and click "Next"
If no drivers show up, then select "Select driver names from a list" and click "Next"
Then select all drivers NOT provided by Microsoft and click "Next"

- Select "Finish" on the next page.

Reboot the system and wait for it to crash to the Blue Screen.
Reboot into Windows, turn off Driver Verifier by going back in and selecting "Delete existing settings" on the first page, then locate and zip up the memory dump file and upload it with your next post.

If you can't get into Windows because it crashes too soon, try it in Safe Mode.

If you can't get into Safe Mode, try using System Restore from your installation DVD to set the system back to the previous restore point that you created.

If that doesn't work, post back and we'll have to see about fixing the registry entry off-line.