Carrot mystery

I wonder if anyone can tell me why my carrot seeds are not even germinating in our "carrot bed"
Around 4 years ago we built a raised bed for carrots. The first and second years were fantastic with loads carrots.
Last year and the year before have been hopeless. We tried this year and we are on the fourth packet of seeds, nothing. We sowed some in the veg. plot with other veg. and hay presto they have germinated within a week. I'm thinking, it must be the soil but I mixed some blood, fish and bone in at the beginning of the season thinking it might help and the veg. plot has blood, fish and bone mixed in.
What are we doing wrong?
Can anyone help?
Please!

i have 2 raised beds both 12ft by 4 ft and i rotate them each year so grow carrots every other year. Been doing it now for some time and its been going fine.   i also put manure every other year , the year i gorw carrots i dont put manure so its doen a year before..works for me

Yes - if you managed to grow carrots elsewhere it suggests that you really need to rotate what you grow in the carrot bed. Peas would be a good crop as they put nitrogen back into the soil.

I cant get carrots to take on our plot at all, yet at home i have five black bins full of carrot seedlings. I have given up with them on the plot now.  mind you the only difference is they have never grown on our plot, ever. 

Are slugs cleaning the tiny seedlings off before you've even noticed that they've germinated?

I've put my "lack of germination" last year and this year down to this. The weeds germinated OK  and I've tried different packets. I've finally got some germinated and have put pellets underneath the enviromesh as well as around the bed.

Yes slugs certainly like carrot seedlings,mine disappeared overnight when i first started growing them.
Try following leeks with carrots in your raised beds,the leeks roots break the soil down very nicely for the carrots.