From the manufacturer:
Legacy Spectra Geospatial GNSS Receiver Firmware Upgrades
Recently, there have received reports of positioning issues with the ProMark 500 encountering an inability to report a position. This is caused by the GLONASS almanac providing out-of-tolerance data for one of the GLONASS satellites. The positioning engine in the receiver treats the almanac as accurate.
This issue has been resolved with the firmware fix which you can download through the link below. This should be distributed immediately to all affected users, as it will resolve the issue with the GLONASS almanac.
I have had numerous calls from users having installation problems with the new firmware over the past week.
I believe this has been due to partial downloads. If you have issues, please use the .ZIP mirrored downloads that I have placed in this web location:
After downloading the ZIP file, unzip to obtain the factory binary file.
Hopefully this is the last update with respect to this issue. (Although I am left wondering about the ProFlex 500 which has not had any new firmware releases.)
iG GPS 
Good afternoon.
I am not your client since I am in Brazil.
I’m getting in touch because I couldn’t get information about my problem, and because of the high level with which issues are addressed here, you may have an answer.
The external buttons on my pm500 receiver do not work.
I have data on this equipment that I need to extract urgently.
Is there any way to turn on the equipment other than through the external buttons?
I thank the attention.
I don’t have any suggestions. Have you tried external power?
Yes, I tried.
The problem is that the buttons stopped working during work, and to turn off the equipment had to remove the battery.
Since then I cannot turn on the receiver.
Consider opening reciever and disconnect, then reconnect the flat cable for keyboard to main board.
There is no service available from factory, so little to lose.
I’ll do it in the morning.
Thank you.
Hello! The exact thing happend to my Pm500 receiver on 13 december. Durring work the screen PM500 blocked, i toke the battery and put it back, but it didin t worked to turn on. I have also information on it. Please let me know if it worked. Thank you.
I own PM500 but I no longer receive the satellite signal Can I help?
Hello sir.
When I upgrade to PM500 appears (upgrade failed) please help solve this problem.