1998 Chevy Blazer door won't close

Sounds like the latch assembly has flipped OR the return spring has broken. With the door open look at the latch where the door striker pin enters it, If the latch has closed the slot will not be open. Stick a pen/screwdriver, whatever in the latch and hold the door handle open, rotate the latch open and see if the door closes now. If it does it again then consider removing and cleaning/lubing the latch OR replacing it.