machine started shutting off after opening while asleep

[Michael Day]

Apologies if this is a FAQ on this list; I did not see such an FAQ and 
wish to be directed to one if such exists.

I've had my titanium G4 PB for a couple of years.  Working pretty well! 
  Last fall I finally upgraded and am running X.2.8.  I use my machine 
so often (it's my main desktop home machine, with added full-size 
keyboard, speakers, mouse, cable modem) that I don't shut it down at 
night or while at work. I just close it and it sleeps.  Within the last 
few weeks, when I open it from sleep, it has started either shutting 
down without warning or giving me the blue screen of death with a 
message that I have to shut it down with the power key.  Could this be 
application-related (I generally leave IE, Word, and the terminal 
program open) or is there something else I should try?

Thanks in advance for all recommendations.  And since my daughter will 
be taking this one away to college soon, I will need recommendations on 
which PB to get next.

Michael