At first glance it doesn't strike me that there is anything wrong with your stanley opener. I would dig out the instructions and go through step by step again. It sounds like the up and down force settings may need adjustment. It also sounds like you may need to reset the down and up stop point. You do the down one first and then the up. None of this will matter at all if your spring tensions are not at or near what is recommended in the instructions. They mention that the door shouldn't rise or fall when you let go of it when it is half way up (or something similar to this, don't rely on my memory, check the book). If the springs aren't adjusted right then your motor will have to exert too much force etc. and it won't work right. Do not adjust the springs yourself if you don't know what you are doing because if they are the overhead type they can remove your hand or head if you don't do it right. Another thought... Is the power (outlet) that feeds your opener on a lightswitch? It sounds like your opener might be losing the stored settings and this can be caused by a power outage or if the outlet is on a switch and the switch is turned off for any period of time.
Also, when the door doesn't work right do the lights start blinking on and off on the unit? If so, I think they are sending a trouble code (ie: 3 blinks etc.) that can be looked up in the book.