I have had similar problems with my 7422GX, and I think I have found a way to prevent the shutdowns. It's not totally convenient but it's better than spending 10 minutes booting and opening all my programs only to see the black screen of death and then do it all over again. Anyway - here's my hypothesis. I cannot guarantee it, but it has enabled me to go for more than a week of heavy usage, with the laptop on for hours at a time, without an incident, which was virtually impossible before. Again, it's just a hypothesis, but give it a try.
Based on what patterns I could see in the sudden shutdowns, I wondered if maybe a particular usage pattern was causing the laptop's internal temperature to rise at a rate that caught the heat sensor off guard. I decided to try keeping the power utilization above or below this "magic" rate. I've read that the processor of this particular laptop runs much faster when plugged in, so I tried using an external monitor so the LCD could shut off and reduce the total power draw. In fact, I cannot remember ever having a shutdown with the built-in LCD turned off. When running on battery, I was able to use the built-in LCD because the processor was drawing less power. However, running plugged in with no external monitor available proved to be trickier. In this case, I tried keeping the power draw ABOVE the "magic" rate. I am a programmer, so I wrote a simple program to keep the CPU at least 75% utilized at all times. Yes, it sounds crazy, but this laptop is fast enough anyways that it was still very usable. I'm currently playing with the percentage to see how low I can go. Hope this works for others.