If the switch has been reset to factory defaults by the previous owner there should be no username and password necessary for console and web access. The default config is for the switch to obtain an IP address by DHCP, so if you don't have a DHCP server then you will not be able to use web access. Then you will need to connect with a console cable and set an IP address manually.
If you need to reset the switch to factory defaults, here is the procedure:
1. Using pointed objects, simultaneously press both the Reset and Clear buttons on the front of the switch.
2. Continue to press the Clear button while releasing the Reset button.
3. When the Test LED begins to blink, release the Clear button. It takes approximately 25 seconds before the Test LED will begin to blink.
The switch will then complete its boot process and begin operating with its configuration restored to the factory default settings.