Thanks for the feedback. A failed Windows service pack installation is the most common cause of this problem, even though hardware issues can cause it. It was unfortunate that you did the memory upgrade at the same time as this gave us additional possibilities
Service pack installation failures seem most likely when you use the MS automatic update. Personally I go to the "administrator" section of the MS update site and download them separately (it's in the options down the left hand side). I then check that the download is the right size before applying it.
I also set the MS updates to download, and then inform me when they are ready. That gives me a chance to turn off the AV and behavioural monitor before installing, and run the installation when nothing else is happening.
If the "black box" is a physical device, it will be a USB connected external drive caddy or docking station. With the docking station you connect it to a working PC and insert the drive you want to work on. With the caddy you install the drive then connect the caddy to a USB port on the working PC. I have one for SATA and one for PATA (EIDE) both are black in colour, hence the name? They support 2.5" and 3.5" drives up to 1TB.
Before you have to go to the extreme step of re-installing Windows, I would try reinstalling the service pack, as there is a reasonable chance that it will work. NOTE: you may have to try this several times before it works so don't give up straight away.
I have changed the thread title to make it more searchable