Blue screen of death incidence gone for now; what happened?

After I reformatted my laptop, I had several incidences of the blue screen of death, although I didn't know anything about it then. (Well I think it is the blue screen of death--the screen suddenly becmes blue saying there was an error, then reverts back to the windows program just as suddenly with a dialog box saying the system's recovered from a serious error.) The last time I had it, I had to reboot--the system wasn't reverting back to windows. For several weeks I didn't use the laptop for long periods, then gradually I began increasing my usage times. Surprisingly but not unwelcomingly, I haven't had any instances of the blue screen of death since then. I was thinking it was because my hard drive was getting old, but logic (faulty, maybe?) tells me I should be getting more instances of the blue screen. Any ideas on what happened then?