i have rb750g using it to load balance with PCC
then it connects to ISA server
there is internet on ISA and also clients
but i can't ping to RB ip " 10.5.50.1" also can't open winbox after ISA

can someone help me with this ?

Not without a network diagram.

Not without a network diagram.

what do you mean with network diagram ?
you mean RB750g Config ?
or ISA Config ?
or what ?

make a drawing of your network. what is '10.5.50.1'? =)