Most likely the internal lithium battery has gone south. Those batteries last some 10 years, and must be replaced after that.
You can check whether or not his is the case by leaving the unit on for a few minutes. It will initially not acquire any satellites because the internal almanac will be way out of date, and might continually ask for initialization options - country, autolocate, continue acquiring. Choose the second or third option (it will keep asking, just keep answering each time). In a few minutes it should find the first satellite, then another, until finally finding your location. The whole process might take some 10 to 15 minutes.
In my experience, even if you don't remove the AA batteries, the GPS will loose the almanac data when you turn it off - demanding another extra long first-fix the next time the unit is turned on. It seems that the almanac is maintained exclusively by the lithium cell , not the main batteries.
This doesn't help with your original question on where to get the 45XL fixed, but at least you might be able to get to see it working now and then.
Good luck,
Bruno.
