hmm... let me get this straight u ran software update for 10.2.3 to get the final version of 10.2 which is 10.2.8. correct?
the thing is you mentioned tiger (10.4)
a fix which usually does _something_ good is to download and reinstall mac osx 10.2.8 combined update
this will overwrite 10.2.3...
in that case hold shift after restarting to "safe-boot" this disables many extraneous startup items/extensions and checks you system for errors.
(be aware that it might seem to take a while as in the beginning the disk check performs without showing anthing. just wait a bit.)
also does it look...
restart while holding command+option+p+r
hold it down until you have heard it chime twice.
this will reset the p-ram (including your monitor settings).
just in case: CMD+OPT+P+R
I suggest you restart you computer holding down command+s
once the black screen and white text finishes loading type: "fsck -fy" and hit return.
wait for the filesystem check check to complete and note any errors. If you got any, repeat the process.
Then type "exit" and hit return. Your computer...