Keith
You need to connect to the USB socket with the K20 near to it (mounted diagonally on the board). This is the debugger interface and your PC sees it as a hard drive "BOOTLOADER" when you hold the reset switch down when powering the board - and the small green/yellow LED next to the K20 flashes at about 1Hz. This BOOTLOADER allows programming different debugger SW to the small K20 (OpenSDA). This USB mode doesn't require a driver since it uses USB-MSD.
I don't know what the pre-installed demo program does (running on the larger KL25 chip). It may have USB device operation but may also not - if not you will never see anything connecting to the other USB socket. I would assume that the demo code doesn't support USB device and then this would be normal.
If you go into the BOOTLOADER drive it has 4 files:
FSL_WEB.HTM
LASTSTAT.TXT
SDA_INFO.HTM
TOOLS.HTM
In LASTSTAT.TXT there is some text showing the status - "Ready"
After loading new debugger code to here it may show error messages, etc. Unfortunately there is no information about whether there is a debugger SW already loaded or which one. However, the green/yellow LED will normally be on when you connect to the USB socket without holding down the reset button and it should again appear as a hard drive - this time with the name FRDM-KL25Z and with 6 files on it.
If the BOOTLOADER appears (reset held on insertion) but FRDM-KL25Z doesn't (when inserted without reset held) it probably means that there is no debugger loaded or you overwrote it with one of the SREC files you tried. The debugger will also use USB-MSD and so also needs no driver to appear as a hard drive.
Did you try updating the boot loader via the "BOOTLOADER" hard drive?
I have attached the P&E that I use. If you drag and drop it on the "BOOTLOADER" hard disk and power up again (without holding the reset switch down) you should see the board appear as "FRDM-KL25Z". Once this is the case you can then use this to load binary files to the actual KL25 on the board.
Regards
Mark