Acer aspire 5100 wont boot even in safe mode

Hello,
i have dis acer aspire 5100-5674 series laptop with both vista business and xp installed in it.
recently i downloaded d windows update in vista..n booom!...m unable to boot from it again..i get this blue screen of death everytime i try to..infact it wont start up even in safe mode..another thing here is that xp is still workin 4 me prefectly..i scanned for viruses n repaired all..can anyone help me pls els i'l throw thid piece out of the window!

Sonal