You can remove the preamp/booster and hook your cable directly to the antenna, to see if you can receive anything in passive mode.
I know you're far out at the reception edge, given 75 miles and the curvature of the earth. I'm a bit surprised at your fairly good reception all these years.
If you're handy with electronics, there are ways to test your preamp to see if it's still working properly. Or, if you have an electronics repair store nearby, they should be able to check it out for you. Since you've been using it for 10 or more years, that makes me suspicious of its life expectancy.
You might also check the various related threads on TV Fool, as probably someone has posted a check and repair for preamps. Or search YouTube for a video. I'm fairly certain you could get some help there.
Here's several YouTube videos to help get you started. They might not answer your issues, but worth a view:
https://www.youtube.com/watch?v=oGHgQE3ztNU
https://www.youtube.com/watch?v=UDOvUN7jzHw
https://www.youtube.com/watch?v=1WK4y2AZXl8
https://www.youtube.com/watch?v=cHWH8mxZuUc
Also, have you done a reception report for your location? Go to rabbitears.info for the most up to date information. You can do a report here on TV Fool, but the last I checked, it still appears to be not as conclusive as rabbitears.info. Although, there's a chance I might be wrong about this.
I'm sorry I couldn't give you a definitive answer to your issues. I'm not a Tech, just my own experiences going back too many years to recall now.
Thanks for your reply. Please keep the forum posted as how this turns out.
If I can think of anything else, I'll update.
Fingers crossed for you!