765t suddenly cannot locate satellites.

Hard reset.

was it cloudy or heavy rain outside?

I find it takes a bit longer when the weather is like that from turning on the GPS for the first time of the day.

Back up the favorites on your Nuvi 765T before performing the master reset.

First, you’ll want to plug your unit into your computer via USB cable. Once it’s plugged in, you’ll want to go to My Computer in your start menu or from your desktop and double-click on the Nuvi 765T.
you will see folders, but you’ll want to double-click on the Garmin folder. Here, you’ll want to look for the “GPX” folder and you’ll double-click on that. In this folder, you’ll want to drag and drop the file titled “Current.gpx” to your desktop to copy it. Now you are able to do the master reset.

To do a Hard Reset on most Nuvi’s
1.- Power off the GPS
2.- Press and hold the right bottom corner
3.- Power on
4.- System asks "Do you want to erase all user data?"
5.- If you answer "yes" next screen looks like brand new device..
6.- The Nuvi 765T should restart and you’ll want to take it where it has a clear southern view of the sky and let it sit for up to 30 minutes to acquire satellites and it's needed almanac data.
7.- once your Nuvi 765T is again tracking and has gathered the almanac data, you can follow the first set of steps again to get to the GPX folder and drag the “Current.gpx” folder from your desktop to that folder on your unit. This will replace your favorites.

Thank you everyone, for your quick responses. It came back on its own, after I left it outside, turned on for about 25 minutes. I have no idea what happened. But I hope it does not happen again.

Mine (a 765T as well) did the same a while back. I had just started driving and it simply wouldn't find any satellites and wouldn't go into the "trouble finding satellites" screen either. I turned it off and on, but it did the same thing a second time.

I don't know if it was sheer luck or if I found an undocumented(?) kind of reset, but here is the last thing I did before it finally started working again (and has been ok for about a month): I turned it off and on again with the switch but held the on switch in the on position for probably 30 seconds or so. While held there the Garmin logo comes up, but it doesn't "boot" any further. Then I simply let go of the on switch and let it continue to boot. It almost immediately found satellites & my position.

Maybe I just got lucky, but it's worth a shot before a hard reset. I didn't want to do that then because I was on my way to a destination that I had previously planned a route for and had saved!

That is a documented "soft" reset.

Be sure to catch the information on almanac & ephemeris data.

http://www.pocketgpsworld.com/howgpsworks.php