Just like Kyle X Y said, go to adobe and look for the trial. Once you're done installing it, it will ask if you have a code. Click yes or w.e it is and put the code it (the activation code from your keygen).
It may say that an error occured and you need to contact phone support. Click ok or find a button on the message that says contact phone support.
It will take you to a screen and will have a hole bunch of numbers. Now if you have a good enough keygen it will have 2 menus. Select the one that says request code (2nd one, on the bottom). Now go back to the photoshop and look at the "request number" (something like that). Go back to your keygen and enter that code into the request box. It will then give you a number. Copy that number, now go back to the photoshop screen. Enter that number in the very bottom. It should say that your copy of photoshop is approved, working, something like that.
Go here for that keygen.
Keygen
Have fun.