There are two pinhole on the Procurve switches: one is reset and the other is clear.
Press the inner button of the Clear pinhole for 6-7 seconds.
Then restart the switch with reload command or plug out/on the power cable.
On next start password wont be asked.
Then you should change the manager password with
if you want to erase startup config
be cautious! this command wil erase all your config.
if you want easy initial configuration.
command will let you config the essential configuration