hyundai matrix

hi a have a hyundia matrix 1.5 TD 02 plate and have bother startin it it just keeps turnin over for about 5 min then sum times starts a have changed the D fillter and checked the glow plugs and the r workin fine if a bump start it it it starts within 10-15 ft every time even after runnin 4 a while i turn it of and wen i try startin it again i get the same bother but sum times a can go 2 it and it starts 1st time but hasnt done this for while now