But my max was specialist without any practice

Yes but only before second contest

Your max wasn't specialist without any practice, it was specialist after the first contest, going down -80 points every contest until hitting newbie.

You aren't practicing hard enough.

I would recommend solve the Div2 B Ladder first and then Div2 C ladder at A2oj. This will most probably show you where you are lacking. Practice those areas.

you have no talent

Oh, come on, what do you expect by just solving 60 A's, 20 B's and few C's ? Huh ?

The community is being pretty toxic... Anyways, practice doesn't decrease your skill, but rating fluctuates a lot. A better question is 'what should I practice to get better?' To answer that better than any random post you can google, you should provide more information on how you are currently practicing and why you don't feel it's working. However, it takes a long time to increase your rating, so don't expect any words of advice that will skyrocket your skill immediately.

Looks to me that your rating is not decreasing in proportion of the increasing of your practice though — it actually fluctuates.

Let's crack down to the mechanics of the rating system. In short, (sorry if this might be rude), but your current ability is somehow around rating $$$1000$$$-$$$1100$$$.

You, as any new accounts, started out with $$$1500$$$ rating — which is way beyond your level. Which means, obviously, in the few first contests your rating would plummet heavily. But, as the nature of the ELO rating system, you won't lose all the rating at one move, so the rate of plummeting was actually way lower (which gave you the "max rating" being specialist).

Throughout the time, when it has plummeted enough, you can see the fluctuation: your rating moves around a certain rating interval. In the case of a newbie, such intervals could be quite wide and the fluctuation could be very unstable due to its very nature: you are at the state of "hit-or-miss", either solve 1-2 problem(s) nicely or not being able to solve it at all.

And the solution to it, well, as people here already stated, is practice. To be honest, around 100 problems are not a huge number of practice in any shape, size or anything. You should try more. Start out with the easy ones first (even some easiest good ol' classics, they can help your implementation skills more than you could imagine), and then increase the difficulty of your training overtime. The process might be time-consuming when you just increased the difficulty, but over time you'll feel it is actually worthwhile.

I stopped participate when my rating is almost newbie
Seem to me that many people did this and never be grey
Maybe you should practice more with hard problems than participate in contests?