iHP-120 suddenly won't boot; ATA error: -1

[Muse]

Bought it used 2-3 months ago, a purportedly little used unit and it's evidently worked perfectly until yesterday. Have Rockbox loaded.

Problem started last night. I didn't drop the player, but did leave it in a warm (not hot) car yesterday afternoon for an hour or so. Temperature could not have exceeded about 85-90 degrees F. Last night, I turned on the player anticipating making a recording and got strange messages:
- - - -
ATA error: -1

Insert USB cable and press a button
- - - -
I didn't have the cable with me, and besides I was in a meeting and had no time to attend to the problem. I managed to turn off the unit (it didn't want to turn off) and tried booting to the iRiver firmware and got this:
- - - -
HDD Full...
please wait
- - - -
Again, I managed to turn off the unit by persistently pressing and holding the stop button and it finally turned off (evidently). Today, With USB cable attached, turn on player and remote shows nothing, unit LCD says only: Bootloader USB mode

Disconnect USB cable from unit, nothing changes. Remote remains back-lit, a minute or so later, the unit LCD goes blank. Unit will not turn off - IOW, remote LCD remains lit but says nothing. Unit will not respond to shut-off command (hold stop button down).

I just had the idea to press the reset. I did, and turned on the player. For about 2 minutes it showed what looked like a pretty normal screen (but it wasn't Rockbox) and it said:

Check HDD connection

Then a screen shows up on the LCD that looks normal but I don't recognize and after 2 more minutes the unit spontaneously turns off.

I turn on again, and the Rockbox boot loader Version 6 screen for 2 minutes and then again:

ATA error: -1
Insert USB cable and press a button

... which I do, and attach the cable to my PC, and nothing happens...

I pressed the stop button, holding it down and it turned off. I then hold down the Rec button and press the play button to boot to the iRiver firmware and it looks normal during the boot process and it again says:

Check HDD connection

A minute or two later it says:

CONNECTED

USB 1.1/2.0 CONNECTION

There's some graphics. My PC doesn't show the device in Explorer (XP Pro), however.

I got a T5 torx bit today and opened the player and removed and reinserted the HD. Same problem. I was about to give up and pressed play one last time and a few seconds later I heard the HD spin up    But it failed to resume playback and then resumed the above behavior. What do you think? Should I test the HD (how)? Should I just buy another HD? Thanks for help.