The extra info that is required:
HP Pavillion DV6 Notebook (dv3112sa)
Intel Core i3
64-bit operating system - Windows Home Premium
-Not a problem when the computer was fresh out of the box.
-No hardware changes.
-Installed some software packages - TSMuxeR, Mozilla Firefox, Mozilla Thunderbird, MediaInfo, WinRAR, Adobe Flash Player, Adobe Reader.....all still working well for a few days.
-Removed the Norton security free trial and installed Avast! antivirus....not convinced that the Norton product is fully removed even after running their removal tool. Some remnants seem to refuse to be deleted via Windows Explorer. Anyhow, still shuttinh down ok for a few days at this stage.
Next bit, in my opinion (though I am clearly no expert), is significant. Ran windows update and installed a multitude of updates, took a long time. Computer was still shutting down ok after these updates but Windows Update then attempted to install further updates the next time I switched the computer on, some of these updates failed and I seem to have had problems since then. Which is why I restored the system to the earliest available restore point, this has not resolved the issue. Also, at the same time as the Windows uodates, I ran the HP update manager which also updated several of the bundled HP rubbish that came with the computer.
Eerrrm.....think that's about everything! As always, any help very much appreciated.