Hey guys I have a Kawasaki Bayou 250 and the brakes don't work. I've taken it to the mechanic and they replaced the brakes and they worked for a little bit but they don't work anymore. Any suggestions on what to do? Any imput would be nice.

Front brake? Back brake? The brakes need adjusting with the cable adjusters every so often. If you don't use them for a while they can stick on the pivot shafts and/or cables.

Its both front and back brakes. I've tried tightening the cable adjusters with no avail so far...... I don't know what else would be causing it.

How long ago was the "brake " work accomplished? If you have adjusted the cables, and adjusted them in the correct direction and they still don't function, then as Merryman mentioned, the pivots are probably locked up ( or close to it ) or your brakes are worn out. I can say this from experience, the 220 and 250 drum brake shoes can be worn out in one hard weekend of riding with a combination of deep mud/water...then fast riding hard braking, and then in the deep mud again. I've have done it....

We do go mudding a lot. How do I check to see if those are locked up. I'm gonna take to to the mechanic again if I can't fix it myself but it would cost a lot of cash.....

Also the choke cable is jammed and won't move. Any suggestions for fixing that too?

If the brake pivots are very corroded, when you apply the brakes, they either won't move ( or move very little and in time will stretch the cables ).....or if they move, they will not return to "non-applied" position. The pivots are what actually moves the brake shoes at the drum. Could be that your brake shoes are just badly worn.
In regards to the choke, replace the choke cable or....the choke mechanism in the carb has corroded in the carb....
Mudding is a blast and I used to do it but...it can be costly maintenance wise unless one can do the work themselves...

Thanks. I'll have to take a look at it. I'm sure there is a video on YouTube on how to fix it or something. Could not riding it all winter cause that too?

Yes to both brakes and choke. Here's a link for a manual for $5. Will pay for itself in a few minutes....
https://www.tradebit.com/G/manuals/14-atv

Yep, riding in mud and water then letting it set for a time will allow the moving joints to corrode or the mud to dry and lockup these pivot areas. Each time you ride in mud and water you need to take things apart to clean and lubricate the moving parts so this doesn't happen. This is one reason I quite doing serious mud riding, to darn much work to keep everything working.