ok I think (my informed guess)youve botched your page file during your reinstal, and xp is setting up a temp pagefile each time u boot, you need to delete and setup a new pagefile, but u cannot do this while the temp one xp creates to boot exists. you need to do this to get out of this
a )reformat and reinstal or
b) boot into your xp cd RC, which is boot to recovery console option prompt
type "cd C:\winnt32" or wherever your xp page file is, check and note
then in this new directory you wil not see your pagefile. sys but it is there, so to make it visible to th RC you need to overwrite it with the contents of another file. this is important so u can then delete so just rename and copy a .txt file over it like:
copy help.txt pagefile.sys
now you want to delete your now visible pagefile. sys
delete pagefile.sys
then type Exit and the system will reboot, when xp reboots it will recognize that pagefile.sys is missing and create a new, good one
so to rehash---from the RC type
cd C:\winnt32
copy help.txt pagefile.sys
delete pagefile.sys
Exit