Looks like you need to just flash/install another ROM. The previous owner might not have wiped and formatted everything necessary before flashing the ROM, which left some residual data behind to corrupt the ROM. Some ROM's have issues with the WiFi radios.
Check and see if there is a nandroid. You can do this two ways 1st By going to the sd card and looking for a folder called clockworkmod, then open it up and find the folder that is labeled backup, then look in there to see if you see a folder with a name or datestamp. 2nd. Go to the recovery menu and look in the backup and restore section. Look in the restore option and see if there is a name or dates stamp.
Until you get another ROM installed, if there is a nandroid to restore, try that. First make a backup of the ROM that is currently installed by going to the backup and restore section and selecting the backup option.
Then wipe and format everything necessary for a new ROM install for your phone. Go back and select to restore the nandroid. Once the nandroid installs correctly you can choose to delete the backup you made by going to the sd card and deleting just the folder with the new datestamp on it that you made.