Before restarting the default server in JDev, you will have to follow the below two actions to make it run it properly again.
1. Change the password in boot.properties
\AppData\Roaming\JDeveloper\system18.104.22.168.37.60.13\DefaultDomain\servers\DefaultServer\security folder, open and edit the password in boot.properties. You can use the inencrpyted text for both user name and password.
For example: changing the password to welcome1
#Mon Jul 18 16:00:02 CST 2011
Save the file and close it.
2. Open JDev, in the right side of it, expand Resource Palette -> IDE Connections -> Application Server, and then right-click IntegratedWebLogicServer, and choose Properties.
A new window pops up, switch to Authentication tab, and update the password there.
After all is done, restart the Default Server. It should be started up properly.