You said that you had trouble fitting the spider. Could this misalignment be causing the mediator/motherboard to bend? This can create real problems with seemingly random instability.
You may want to check the backplane of your tower is not bent, casing the problems in fitting the card.
Also - are you using any unpowered hubs or any other unpowered devices? The spider (iirc) does not like to power devices of more than 0.4A through any USB channel.
Regards
Rich
