Workaround - power down the machine for a few minutes. Reason - don't know, but it seems to work sometimes when simple rebooting doesn't. Incorrect parameter RAM settings. Reason - bad settings can result in improperly configured hardware and software. While this list isn't complete, let's see what we can quickly figure out about what's happening here.
Possible causes are too numerous to mention.
It's hard to write system software, and that's what extensions are - system software. Extendibility makes the Macintosh interesting, and it comes with a price. Might also be that something needs to be reset but doesn't except during a cold start. Someone or something writing to PRAM unintentionally or incorrectly. Power failure comes in many forms.