windows/firefox problems....Plz help soon

hi guys
i have been facing some problems,i am at my wits ends after doing so much trouble shooting and still no solution.i am highly seeking your advanced answer to these problems.
1.i have been facing windows update.exe error saying "windows update.exe has encountered a problem and needs to be closed........" i am using windows XP sp3,and i dont like updates,i have just turned them off,but for this problem,i turned them on but still problem exists.
2.this problem is with firefox.i am running an updated version with all addons updated.firefox version 8.0,when i close the firefox,it stays in taskmanager,and doesnt exit completely.though i dont have any problem in running it or browsing but it stays in task manager and doesnt exit,and at startup of windows,it always gives an error message saying that "firefox.exe has encountered a problem and needs to be closed.........."
3.upon shutting down windows,there come a ding,and an error comes,but then windows shuts down(as normal) and in that blink i cant see the error,what does it say,i dont know what is that error.

i ran regcure software to fix registry problems but still all problems exist.kindly suggest me solution

but dear,the problem is related to windows platform,and atleast firefox issue is not related to OS,please help me if u know something,i will be greatly thankful.