hi
it may be three reasons
1]connection problum
2]battery saver mode
3]if we first time when configuring facebook in windows phone then we need to allow some access to facebook,if we reject those access then we cannot chat,for solve this issue first remove facebook from phone(via emails and accounts)then logon hotmail id via pc,after login hotmail id there is a downarrow in the left top side of the screen,if we click the arrow we will get people tile after clicking people tile another window arrive with phone no and all seel the right side there is written connect to facebook just click that icon another window will pop up,see left down side there is an option for remove facebook account,problum solved
after remove facebook from hotmail id just reconfigure it in phone u can able to chat
some grammer mistake and spling mistake may arrive
Thanks