Step 1) Open screen resolution settings & select the detect button. Step 2) Find the adaptor in the list of manually detected displays.
 
Step 3) Choose the toption for "Try to connect anyway on: VGA" Step 4) Apply the change.
 
Step 5) Now choose the extend or duplicate display option. Step 6) Apply the change.
 
Step 7) Almost done. Step 8) You may need to modify your cc_config.xml & add the use_all_gpus option before restarting BOINC.