I had a very similar problem. The card would work for anywhere between 5 minutes and several hours, but eventually always stopped working requiring a reboot. I tried flashing the firmware and installed a later driver (2.1.39.0) which helped, but did not solve the problem. In the end I contacted Paul Pang who was surprised, but very helpful. At Paul's suggestion I returned the card and ordered the V2 card which he sold me at a reduced price. This card works fine ( I have over 500 hours on it) and sounds great. I have also bought Paul Pang's SPDIF converter. The two together are fantastic.I would suggest doing a search for the most recent driver for the NEC 720200A chipset and trying that.