OS 8.6 conflicts?

[THE ROCK]

I upgraded the OS in my 3400/200 powerbook from OS 8.1 to OS 8.6. Now
I'm noticing some problems that I did not have before. When I launch I.E
5.1 the brawser does not completely launch but kind of get's stuck
midway. All I then get is some kind of buzzing some. I here the hard
drive turning or trying to, then the buzzing sound. This goes on until I
turn the computer off; using ctrl ,open apple command, power off button.
There was no problem under OS 8.1. I just installed MS office 2001. Word
has the same problem when I try to quit out of the program (office 98
worked fine in OS 8.1 and 8.6). Help.
TIA.
Peter.