Yesterday i changed my Athlon 3200+ cpu over to a dual core Athlon X2 4200+. The thing was that my existing Windows XP Pro installation was without ACPI enabled therefore i had a maximum of 15 interrupts and only one of the two cores was enabled at windows (windows task manager showed only one cpu graph).

quick search to the internet showed that the only feasible solution was to re-install windows

...solution i was not very happy with...

Further search revealed that the missing "halmacpi.dll" was responsible for my troubles and this could only fixed by installing windows...

...well WRONG!!...

just follow the procedure described in this page here...

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