Im trying to fix my cousins comp he tried to format the hard disk and it stopped half way through the format. He then tried to load a xp upgrade disk which he found he had no key for. It is now caught in a cycle of starting and shutting off it starts by saying setup is being restarted then the error: "insufficient system resources to complete the api" then restarts
............ how can I get into dos to format and start again

Hi welcome to PCHF You should be able to boot of your XP cd and repartition and format the drive then continue to install xp. You will have to set the PC's bios to boot off the cd. If that fails get a boot disk from Bootdisk.Com and boot off that and delete the partitions and recreate them and format the drive then install XP