XP NOT RESPONDING

I just reinstalled a fresh copy of Xp home SP1 because my sister was at my
home downloading crap like crazy and alot of it would not remove. To make a
long story short....i only have basic programs on it now.....but it seems
every time i open a program it stops responding and i have to close and
sometimes reboot........the programs that are not responding are IE, Task
manager, norton, and many more.....i have done a scan and there are no
bugs....what do i do? How can i fix this without ANOTHER reinstal?

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