This is similar to the "Poly Evolver Keyboard dropping notes or has a dead voice" article.
If your Poly Evolver Keyboard is freezing on startup, it is likely one of the socketed voice PICs (chips). The most common cause for not starting up is the voice 1 PIC losing communication with the voice board. They are socketed chips so occasionally this happens. You can check this easily by removing the 4 screws on the top of the PEK and looking at the voice board in the tray. The voices are clearly labeled and the voice PICs as well as the DSP flash chips are the only socketed chips on the board. Press firmly on each one of them (there are 4 voice and 4 DSP total) to make sure they are well seated. You may not be able to physically see or feel them move, but it doesn't take much for a pin to lose contact on such a small level.
If that doesn't work, you can try swapping the voice 1 PIC for the one next to it which will often fix the issue. You can get the chip out by using a chip-puller (best), and if you don't have one there are two other methods that work well. You'll notice there are 2 slots on opposite corners of the sockets. You can use 2 small flat bladed screwdrivers on opposite corners and slowly work them back and forth, or a straightened paperclip with the very end bent at a 90 degree angle with pliers also slowly working opposite corners. Go slowly and take care not to damage or break the sockets.
Once you get the chip out, just bend all the pins away from the body slightly (making sure they are still aligned). You can use a small set of needle-nose pliers, or a small flat-bladed screwdriver will work too. Applying some electronics contact cleaner to the pins and the socket can also be very helpful.
Reinsert the chip in the neighboring socket and see how it responds. Chances are your Poly Evolver will be working properly. After doing that, you may want to update your OS to the latest versions, as there have been a few changes regarding voice stability: