I have been using a PR System one for 4 years and recently left it on a train in southern CA. (yeah for me!!)
I bought a PR System One 750P used that had under 100 hours on it, although old, it looked brand new. First night with it home - i was cleaning it before first use and took out the sd card. I was going to look at the data in sleepyhead and try to delete or reformat, but couldn't get anything to load. I checked and there were files on the disk and text files. After cleaning the machine I plugged it in and it started to boot. LED Display came on and it got to the standard screen(Therapy, info, settings, bi-flex). I was going to go to info and then realized i had not put the sd card back in. I put it back in and all of a sudden i got a single beep and it rebooted. It is now stuck in a reboot loop. Display shows logo; then Ver.2.02; then 7.0 cm h20; then 11.0 cm h2o; then a straight line; then a beep and then loops back to start again. Doesn't matter if i have card in or not, just keeps looping to start again. No LED lights when this loops. have tried unplugging and letting it sit. but it does the same thing. Anybody have any suggestions?