Hello necessary to enable the DHCP but through WinBox not know the password need to reset the router so how? Please Consult
Use Netinstall: http://wiki.mikrotik.com/wiki/Manual:Netinstall and reinstall the OS, making sure not to check the “keep configuration” checkbox.
Or look up the manual for the exact model (500 is a series of models, not a model) and look for a configuration reset jumper. Not sure if the 500 series had these.
Warning: this deletes ALL settings, not just the password. You will have to reconfigure everything from scratch.