nuttynibbles

hi, i recently repair my computer w/ window xp pro cd..after which i dl service pack 2 and did the rest of the updates required..then i restarted my com and explorer.exe could not start during startup. i had to go to task manager and run it from c:/windows/explorer.exe..i restarted my com several time but the same problem persists.. how can i solve this problem?? many tks!!