Toshiba A100 -147 won't load xp

[notanexpert]

My Toshiba A100 - 147 suddenly refused to boot into windows XP, it shows message "We apologise windows did not start correctly......" gives options, safe, load last good.... start windows normally etc, but whichever I choose, the machine just trys to boot windows then after the logo screen with the moving bar below, it crashes to start it all again. If I leave the machine alone it will continue to do the same thing time and again. Any ideas please?