More recently introduced terms such as 'annually laminated' are synonymous with varve. Of the many rhythmites in the geological record, varves are one of the most important and illuminating in studies of past climate change. Varves are amongst the smallest-scale events recognised in stratigraphy.
PCs are designed to shut down automatically when heat endangers the hardware. To find out if this is your problem, download and install Speedfan. It's small and free. Although Speedfan's basic job is controlling the speed of your PC's fans (you probably guessed that by the name), it also provides the CPU temperature.
Simply get into the habit of pressing your PC's power button instead of using any of the methods above to actually shut down your machine. If you have a laptop, you can merely close the lid to put Windows into sleep mode, but using the steps above you can change what that action does, too.