Windows 7 BSOD when switching on computer! Then worked ok?!

Hi Bluejen,
in order to effectively help you we need to see your dump files. These are created at the time of the bsod and are found in the Minidump folder. This is found in the main windows folder on the C drive. If you can't find it you probably need to change your settings so that the machine is configured to produce dump files:

Go to Start and type in sysdm.cpl and press Enter
Click on the Advanced tab
Click on the Startup and Recovery Settings button
Ensure that Automatically restart is unchecked
Under the Write Debugging Information header select Small memory dump (256 kB) in the dropdown box
Ensure that the Small Dump Directory is listed as %systemroot%\Minidump << where your .dmp files can be
found later.
Click and apply to exit the dialogs,

Once the settings are changed you'll then need to wait for another bsod. If you already have dump files ( we always prefer more than one if possible) then please read this thread:
Link Removed
This just advises on how to gather the information we need.