Dap-1330 no internet connection

Please I really need help with the above extender, I flashed for my first time openwrt firmware, but I can't make it right. Before flashing the firmware the extender was working, now I can't configure it to get internet connection.
Router is at the 1st floor, second floor we have the extender, lan cable attached to my desktop from extender to desktop (no WiFi card)
I can access to the extender, scan ,join network (router) but my desktop and extender won't give me internet.
I also would like to know if there is any chance to flash the stock firmware back.
Thanks for your help.