Sorry if this is the wrong area. I never know where to post anything anymore.

I've been playing guitar now for about 4yrs and i cant write. I become dumb founded when I try to sit and write a song, lyrics or music. I just can't to it, everything I come up with ends up being exactly like something that is already written. and when ever I pick up a pen and paper I just end up staring at the paper with nothing coming to my head. I also have trouble finding a melody. I don't know why. I just Cant do it. Any advice?
For me writing is like meditation. I need to sit down and have nothing on my mind. Just have myself, my guitar, and a pen.
For some people the writing process is easy. For others, its downright brutal.
The best thing to do is to channel your feelings. Play around on the guitar and come up with something - don't worry if it sounds like something thats already been done, most music is like that anyways - the real difference is when you add your personal touch to it.

If you can't find that 'personal touch' or don't know what it is - for me, its what sounds good to ME. When I write and play music I play it for myself. If I am happy with it, then thats awesome. If other people dig what I write, even better. But first and foremost, I write for me. And I don't care what other people think. Let your inner thoughts run.

There is a famous quote --

“The mind is sharper and keener in seclusion and uninterrupted solitude. Originality thrives in seclusion free of outside influences beating upon us to cripple the creative mind. Be alone—that is the secret of invention: be alone, that is when ideas are born.”

Thats how I do it.

Hope that helps man,
I never "just sit down and write." Its probably impossible, although, i'm pretty sure John lennon did. But no one likes him anyways, Right?! Usually when i'm just jamming i will come up with something that I deem worthy of the public ear, and write that down. And when it comes to lyrics, write about something that affects you in some way.
And regarding you thinking it sounds like other music, errol garner thought that misty sounded like a song by someone else, but it wasn't, and look how popular it is. Paul McCartney had the same problem with the song yesterday, i believe.
You sound like you're taking the fun out of playing. Hell, you're not even playing anymore, you're trying to write! That is where your problem is. Play. Remember when you would play tag as a kid? You did it cause it was fun. Do this here. Pick up your guitar. And. Play. Don't ever force anything... it doesn't work. Trust me.

Don't worry about if it's already been written. If it has actually been written there are MANY ways to change it so it doesn't sound like it was originally made by whoever came before you.

Learn theory if you already don't. Believe it or not, your studies will inspire you. You'll learn something new, hear an example (or not), and all of a sudden something will pop into your head. That's how it works.

Above all... just enjoy playing.
I occasionally find that the guitar itself is hampering my creative process. It's like I'm so used to playing patterns or in specific styles that I start to repeat myself or run out of ideas if I'm just jamming away.

Try putting yours down and hum to yourself or try to write a riff or melody or progression inside your head, or just start humming random melodies. Once you've got something worked out that you like try to figure out how you'd play it on a guitar.

Also most ideas have been done before. so if you come up with something that sounds like something that's been done before don't worry. The trick is to taking something unoriginal and turning it into something original through use of rhythm and melody.
i had that problem before...it takes something special to write a song..both guitar and lyrics...and its a feeling thats comes and goes..

my best advice to give you...never make something up for someone else to hear...make something FOR YOU TO HEAR. dont deem a song worthy for someone else...its for yourself.
it comes from your heart and soul. hell its music you play for you..and no one else..

when you make something up that you like YOU KNOW YOU LIKE IT..and naturaly this will come to you as a musican you must learn to respect the music..for you to play it..its truly a gift.

iv never said..im going to write a song..and acutally wrote a good song..it always sucked...but when that mood kicks in..and you get chills..thats what your looking for..

and its the same as lyrics..you get better over time learning to express yourself thro words..id start with poems

my heart was broken when all my strings broke.
so i went to my room and snorted some coke
tho i had no money and felt no fear. i
know my time would soon be here
tomorrow was friday i should have been happy
checkin out the guitars noticed people laughing
i payed no attention till i got home
and noticed that there was coke on my nose