Assuming you don't have an external backup, your best bet would be System Restore. If that doesn't work, you'll need to save your data and restore to factory settings using the discs that either came with your system or the ones you made according to your user guide.
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By the way, I guess you're aware that Microsoft is pulling the plug on the last remnants of support for XP next Tue. 4/8/14.
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Good luck.
hello my name is lisa i need some help.today for some reason i went into the control panel and messed with the desktop,theme,and other settings now the pc is actting different and i seen a pop up saying something about useing to much power.I tried to restore but it wont a few months age i let microsoft have control to my pc and try to help me the worst thing i have ever did.My question is can i reset my settings to default or is there something else i should do thank you lisa

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