MacBook Air early 2015 doesn't recognize UBS from LG27UD88

Hi all

I have a MacBook Air with early 2015 which has a thunderbolt 2 port. I bought the 4k LG monitor LG 27ud88-w.

I connect the Mac using a thunderbolt 2 to DisplayPort cable with the monitor. Heres the prob

1) I can get the display, however the usb and other ports at the back of the monitor arent getting recognised by my MacBook. so I cant plugin my mouse etc in them

2) I see in my sound (under system preferences) that LG is a output. however when I select that, no sound goes out to the monitor.

I have restarted, reconnected, updated the LG to latest firmware.. and still doesnt work. can someone help please

appreciate that

rgds

T