Hi,
First of all 5120 was not a part of the former ProCurve brand. It is a Comware based device (former H3C)
As far as I know there is no Reset button on this switch.
You need to establish a console connection with the switch.
Then at some point you will get the message similar to "Press Cltr+B to enter the Extended Boot Menu". This has to be done within 5 seconds after the message is displayed
After you do thath you will enter the boot menu. It should look like that.
Password recovery capability is enabled
BOOT MENU
1. Download application file to flash
2. Select application file to boot
3. Display all files in flash
4. Delete file from flash
5. Restore to factory default configuration
6. Enter BootRom upgrade menu
7. Skip current system configuration
8. Reserved
9. Set switch startup mode
0. Reboot
Ctrl+F: Format File System
Ctrl+P: Skip Super Password
Ctrl+R: Download application to SDRAM and Run
Ctrl+Z: Access EXTEND-ASSISTANT MENU
Enter your choice(0-9):
Option 5 should provide the desired reset to factory default.
If access to the CLI of the switch is possible it is also possible to reset the switch with the command
<5120> reset saved-configuration
<5120>reboot