I have been noticing this more lately. For some reason, the start button at the lower left corner and the WinKey both, when struck, will not cause the Start Menu to appear.
This is always temporary, and if I wait long enough, several minutes at most, they always begin working again and continue to behave normally for long periods of time until the behavior recurs.
Is anyone aware of the reason for this behavior, or if there's a fix. There's so much information out there on Start Menu "won't open" problems but nothing I've found that really matches this description, as most seem to describe a "permanent" problem until fixed and mine is not permanent and is, in fact, always transient. It is not occurring during system startup, nor when the TrayStatus 3.1 utility I use is showing any high disc activity or the system is loaded with processing that's CPU intensive.