MasterPage By Mistake revert in v3 how to reverse back in v4

Hi,

By mistake i set to my customize master page as set as default  the senario is as follows

following is the Custom Site http://mycustomsite/sitepages/mycustompage.aspx i remove site action link from so i use default master page for site action as folllowshttp://mydefaultsite/sitepages/home.aspx i remember i just change to mycustompage.aspx as default page in Masterpages after that i can not access to myhttp://mydefaultsite/sitepages/home.aspx and aslo if i open the same in sharepoint designer it shows 2007 masterpage instead of 2010.

Any one can help me, Thanks in advance.

Regards

TeeJay