It could be you don't have enough memory.
However, if the entire computer crashes, there could be other hardware causes, such as a fan malfunction that causes the CPU to overheat. Another possible cause is malfunctioning memory chips.
It has been noted by Adobe employees that you will probably get your best HDR results from using just two images. Try that, and see if the computer handles it properly.
Thanks for the feedback. I'll certainly use fewer images in future, certainly seven is extreme. But I might also say Photomatix handles the same number of files with grace so for now I'm back to Photomatix.
I thought I had the same problem. I have a middle of the pack computer and was trying to merge 5 shots. It did not seem to work and seemed to freeze the computer. Then on another try I was called away and came back 20 minutes later and found the shots merged. I suppose with more memory or a more powerful processor it would take a minute But I learned it wasn't the software. So my advice is try again and go wash the dishes and see what happens.