but no oneแต่ means “but,” while ไม่มีใคร means “no one” or “nobody.” It is used to introduce a contrasting situation in which nobody does or knows something.
TH: ฉันพยายามขอความช่วยเหลือ แต่ไม่มีใครสนใจ
EN: I tried to ask for help, but no one paid attention.