ok today i was out riding my mt bike on trail.

All of a sudden, chain jam, so i had to get off bike, only to find that my middle ring was broken.

like one part was totally broken away and rest was bent.
I have no clue as to why this happened.
Is it possible that when i installed it , it was not tight enough as the other bolts were all loose.

It was a newer chain ring as i installed it a few months ago with no problems.
well back in May.
it was working fine as i was riding on it quite a bit with out problems, but the odd times chain would skip here and there.

So why would this happen?
do replace? should i replace the entire crankset? or just get a new middle chain ring?

As even as i can ride in the lower ring and the big ring, but my chain still skips

i have a newer chain and the rear cogs are new as well.
just the front is a bit older
derailleurs are older shimano XT and are set fine,
so what is the suggestions?

just replace the chainring and chain .sound like the chain is bent too .

It is a brand new chain though.

I took apart a shimano deore crankset to clean it once, and what i did notice was that there are very slim brass washers between the chain-rings bolt holes. I lost one, but re-assembled the crank without that one washer. I havent had any probs with it coming loose. Maybe these washers are missing from your crankset? I wonder if that is the reason your middle ring came loose in the first place?

I will have to take a look. Perhaps buy some new ones.