Very slow, no sound, is it repairable?

Well, a number of things can be done, if the computer is running slow, open it up, and while it is running, feel the heatsink for the CPU (After grounding yourself) and see if it is hot. If it is excessively hot, look at the two clips that attatch the heatsink to the CPU, and see that they are snuggly attatched, since these do have a tendency to slip off over time, and if they become dislodged, the cpu will not make proper contact with the heatsink, thereby slowing it down drasticly. If the system's drive is full, than you might want to delete some files, or get a new drive. Also, if you are experiencing slow booting, you might want to reset the NVRAM, to do this, boot into open firmware (Turn the computer on, and right after the chime, hold "Command[apple]"+"Option"+"O"+"F" simutaniously until you see a white background with a prompt with "ok >' In the prompt, enter "reset-nvram" and hit enter, then "reset-all" the computer should reboot. This might speed up the computer, if it hasn't been done within the computer's lifespan.