Boot up loop

Hello,

i have a rather big boot up problem,

my pc goes though its buisness but then displays the "windows failed to start, this may be due to a recent harware or software change" and you know the rest but no matter what option you choose it just keeps doing that,have loads of photos and important files on there and i afraid that i may have to wipe both hardrives i also updated my graphics card driver about a week maybe 2 before it went wrong and the day before it went wrong it rebooted because it encountered a crittical error also the games i play on it non-online keep crashing and displaying a message about stoppoing because they tried to execute code in the windows system files

i really need help on this

my system is windows xp professional
it has a 256mb ddr-sdram
40 gb ultra dma hard drive no idea what the other one is