Workgroup instead of domain

Hello,
I went into control panel-->System-->computer Name--> change--> and changed "member of" from domain to workgroup (radio button) and typed the workgroup name in the space provided... I did not change the computer name. The computer asked me to reboot and when I did I could never log on again... my username is a0196053 and computer name is DTA0196053 while workgroup is dweiknetwork and the domain name used to be ent ... what should be my login name (like DTA0196053\a0196053 etc...)... can I log on the system without any workgroup or domain?