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it might have become corrupted and would need to be reinstalled
but there is something pretty simple that you can try that might work if it was working yesterday. you can restore your computer to the way it was a few days ago. it is very easy to do and fully reversible. if it doesnt work please just get back to me and we can try some other things. I can even log into your computer remotely to fix it for you if necessary. But there is an extra charge for that so lets try this first.
SYSTEM RESTORE INSTRUCTIONS - XP VISTAstart menu / all programs / accessories / system tools / system restoreselect restore to an earlier date
you will get a calendar with various restore points for each day
choose one for a date BEFORE the problem started
hit the ok /restore button
the system will start to shut itself down and a blue status line will come up in a box saying restoring your system settings.
when it finishes the system will restart itself.
hopefully everything will work the way it did on the date you selected