MY HP 6910p runs extremely slow, CPU usage very high...
Use the built-in tool to check RAM, HDD - OK!
Using clamav to scan for virus, msconfig check - OK!
Symptoms: 100% CPU usage, battery not charged. After charging overnight, still below 10% charged.
Solved: By replacing AC adapter and the battery.
My Comments: When the AC Adapter cannot provide enough power, the CPU performance drops and so the 100% CPU usage. My situation is more complicated because both the AC adapter and the battery are bad. In your case, may be just changing the adapter will solve the problem.
Google this problem shows that I and you are not alone. Hope this helps you!