It has just occurred to me that your using a similar set up to mine...
A1200 Blizzard060/PPC 60Mhz/240Mhz / 256 Meg Ram / 2 500Gb HD's /2 DVD burners / FASTATA MKII
I had forgoten that I too had the same problems as you (it was almost 5 years ago). When I first got the Blizzard board I tried it in one of my desktop A1200's. Same thing, sometimes worked sometimes didn't mostly a black screen. I desoldered the connector and fitted a new one (not an easy task).
Still had the same probs, Then I built a tower and stuffed everything in there. Now here's the thing, I used the power supply from one of my old A2000's, It worked but still quite randomly the black screen problems and such kept popping up.
I finally solved the problem by putting in a new bigger power supply and have never had any problem to this day (fingers crossed). If I recall the A1200 supply was around 200Watts, which you would think would be enough but with the new PSU I put in 350Watts the problem was solved.
It was all down to the -12Volts. On the old A2000 PSU it only gave out a max of -12V at .5amps (if i recall correctly) while on the new 350Watt PSU the -12V supply is 1.5Amps.
Like I said since then I have run the above setup and never seen the problem since.
Dunno why I didn't remember sooner, guess I must have managed to forget about it.
Cheers :drink:
Franko