Rhythm

You are counting when you play, right?

I am trying..And most of the times yes... But the problem is at songs that use strumming.. I cant get into the correct rhythm

just buy a metronome (or google for an online one), and count 'one-and-two-and-three-and-four-and' to the beats of the metronome, then work on getting your picking hand moving in time with your counting.

If youre strumming then your hand should keep moving, even when youre not actually playing the strings. Your hand should reflect the beats of the metronome.

The example above refers to playing 8th notes, so each measure is split into 8, and each part of the 'one-and-two-and-three-and-four-and' equals one 8th note. You'll find that different songs are sometimes divided differently, like perhaps into 16th notes, but I'd start with 8th's first.

Nothing is 'genetic' with this stuff, its all practice mate.

The problem is , I can do coreectly exercises with metronome, but when the time comes to play a song then i mess it up :/

I was just going through this with my teacher yesterday. It's been 20 years since I've actually played an instrument, and any rhythm I had has left me. :P Slow tempos have always been tough for me, and the exercise he has been having me do are much more difficult for me as quarter notes at 60bpm than at 120bpm. I lose the beat and then my picking pattern.

When we stopped the exercises to talk about it a bit. He said not to think of the beat just as beat-beat-beat-beat, but as a part of something bigger, part of some sort of process. The image that works is different for different people. For some people, thinking of a spinning wheel works, for others a swinging pendulum, that kind of thing.

Then turn on your metronome and listen and think of the wheel or whatever. Don't look at the metronome, that just adds tension and makes things harder. After everything lines up in your head, figure out where in your body you feel the rhythm. Another thing that he said is different for everyone. It might come from tapping your toe or heel, or nodding your head.

When you are working on exercises with the metronome after this, don't start playing immediately. Just go through this process for a measure or two of beats, then start playing. It'll be easier to get into the groove each time you do it, and then when you're actually playing with others you should be able to do it just from a count. If you're playing with others and no one counts before you start, just ask them to.

It made a huge improvement almost immediately in the lesson and in practice afterwards.

When you are playing with other people, is there a bass player or drummer that you can follow - kind of a substitute metronome?

When practicing with the metronome, sometimes change it up. Set it to only click on the even beats, or only on the 1 beat, and try to keep your rhythm going steadily during the "quiet beats".
Record yourself practicing, then listen back to it.

Also, can you give us a bit more information to go on? The more we can understand tour problem the more useful the answers will be.
What style of music? Perhaps tell us a couple of example songs.
Can you post a recording of the problem you are having?
How long have you been playing? Do you have a teacher? When you play with others, what instruments? Are those players more experienced than you? Or less?

Try humming or singing the song before you start playing so you feel it. As corny as it sounds, rhythm is all about feel. Get the song in your head and you'll be able to translate that to your strumming.

if you're having trouble with a rhythm, stop, hear it in your head, and try again. if you're still having problems, try playing along with the record until you sync up and then try again on your own. you can also just play until you find your natural rhythm, and use that to work from and develop more rhythms.
but regardless of your approach, keep plugging at it and it'll come to you.

All of the above advice is good, and essential. I won't repeat or re-word, but encourage you to keep at it, and it will come. :D

Try humming or singing the song before you start playing so you feel it. As corny as it sounds, rhythm is all about feel. Get the song in your head and you'll be able to translate that to your strumming.

I do that a lot and it helps me keep the rhythm going. Hard to explane also... but I "see" the missed beats as notes also... just ones not played... everyones mind works a little diferent though. As was said, I also have a harder time doing it at slow speeds... I HAVE found that slowing it WAYYYY down to work through it.. then going back to what speed fits for you helps also... Mostly I do best when I just stop worrying about it, and let my hands find it. :D

The problem is , I can do coreectly exercises with metronome, but when the time comes to play a song then i mess it up :/

You are having trouble being "in the moment" and not with your timing. You have to "be" what you are playing. Once you do, you'll feel it...you'll play it...and you'll know it.

Cat