Frequent start up or shut down problems?
Stop errors or BlueScreen problems can arise at start-up times or at shut downs due to innumerable reasons. A few scenarios are discussed as under: 

• You install a third-party driver and you get a BlueScreen on start up
• On shutting down your Vista, you receive errors
• You remove a USB host controller and get stop errors

In the first scenario, if you install a third-party driver that manages on-board flash memory for ReadyDrive, your system may experience a low memory.  A large amount of memory is used by the Ecache.sys driver, already present in Windows Vista, while caching data during the boot process. If this doesn’t happen then data will be directly read from the hard disk drive.

The cached data improves start up times. When you install a third-party driver, the memory is loaded and hence the data is not properly cached while booting. Then, you end up with a Stop error message that states:  

 STOP: 0x0000007F (parameter1, parameter2, parameter3, parameter4)

UNEXPECTED_KERNEL_MODE_TRAP

Also, at times your Window Vista can give the following error messages while shutting down:
Stop 0x00000050 (parameter1, parameter2, parameter3, parameter4)
PAGE_FAULT_IN_NONPAGED_AREA during the shutdown process

This error happens when the memory manager tries to zero out all page files. By mistake, the memory manager sets a wrong flag to the header of a Memory Descriptor List (MDL). This lets other drivers to access the zeroed memory space causing the error.

While removing a device that contains a USB host controller or a USB host controller itself your Windows Vista may crash at times. You may even receive a Stop error message on a BlueScreen. This may happen if data is transferred from the USB device to the USB host controller or if a USB device is connected to the USB host controller.

Some other problems that may appear if BlueScreen or stop errors do not occur such as:

• A black screen appears when you close Windows Vista. To resolve it, you have to manually turn off the computer
•  The USB host controller does not appear in Device Manager, if you connect the USB host controller again. The USB host controller and any attached USB devices do not work.

Ask PC Experts suggests that these problems occur due to issues with the USB hub driver. 

How to fix BlueScreen or Stop errors?

There could be software or a hardware issues leading to BlueScreen problems or Stop Errors. Sometimes, when a program stops working, Windows can fix a problem or find a solution. You can also check if Windows has found a solution by following these easy steps:   

1. Click on Start, and select Settings. Then click on Control Panel.
2. In the Control Panel, click on System and Maintenance, and click on Problem Reports and Solutions.
3. In the ‘Problems Reports and Solutions’, dialog box that opens, click on Check for new solutions in the Tasks pane (on the upper left side of the window). As soon as you do that, Windows will check for solutions.
4. If a message is displayed indicating ‘No new solutions found’, click on Close. Or, if any links appear under ‘Solutions’ to install or Information about other problems, click each of the links and follow the steps provided to solve those problems.

For Microsoft Windows Vista troubleshooting, you can always look up to Ask PC Experts. Just dial toll free number 1-888-889-335 for instant assistance. They have flexible pay plans- annual and incidental that you can choose as per your budget.