I recently developed a problem with my Mac system and am looking for ideas. I am running a Mac Mini, about 4.5 years old, that has a 1TB fusion drive, connected by Thunderbolt to a LaCie 5Big and an NEC PA272 monitor. For several years, this has worked perfectly, but recently when the computer is turned on, I am able to log in, but then the monitor grays out (the "wallpaper" appears but looks as if this image is covered by a veil; the dock does not appear; and nothing is clickable). This, happened gradually over the span of several weeks, until it could not be solved by restarting the computer. The situation occurred in conjunction with a pair of redundant hard drives on the 5Big filling completely, but I don't know if that could be related. I can still use the computer, but not when the 5Big is on.
Any ideas?