Mac beach ball problem.

Hi everyone,

I have macbook pro mid 2012, i7 processor, 8GB of RAM, 750 Harddrive. It was running perfect, I partitioned the disk into two, and made one partition full with movies. Before it was OK, it start becoming slow so, I think it might be because of no disk space on one of the partition. I bought external harddrive and transfer all movies to that harddrive. It was still slow so I formatted the harddrive, made it one partition and install mavericks. It still shows the beach ball problem. I did hardware test, RAM test. All was fine. I tried to recover to mountain lion but the internet was slow so it could not be downloaded, also my wifi automatically disconnects after some minutes so l have to reconnect my wifi and start the download. Please guys help me, what is the problem with my mac?.......