Macbook Pro Sleep problems

Hi everyone,

I've got a 2009 Macbook Pro running Snow Leopard.

Putting the MBP to sleep by going to the menu and selecting sleep, as well as pressing the power button and selecting sleep works perfectly fine! The MBP goes to sleep as expected, and i can close the lid. When awoken from sleep, everything functions as expected.

However, the problem comes about when I try to put the MBP to sleep by closing the lid! The MBP does not go to sleep. The screen remains on and the apple logo on the cover remains lit. Opening the cover, the screen is still on, and all functions do not work. The trackpad does not respond, the keyboard does not work, nor does an external mouse (if connected). I then have to forcibly shut down the MBP by holding onto the power button.

I've tried all the PRAM and SMC reset suggestions, but to no avail either. I've even tried sending the MBP back to apple for repair, but it has not helped.

I've been searching for similar issues but have yet to find anything that really helps! Hoping someone has experienced and solved this!