Framiga,
One last try about the 604e (this just crossed my mind).
Turn on your Amiga and quickly try to run a PPC program and see if it works. Make sure that the accelerator itself hasn't been used for a while and is completely cool.
It could be that your PPC chip gets overheated pretty fast and needs some extra good cooling. This is of course a long-shot guess, but it's worth a try. I've seen PPC cards do this (e.g. the provided heatsink and fan are simply not enough, as there are revisions of 603e and 604e chips that just get way too hot after minutes of usage, or less).