The very same thing happened to me a few days ago, running the same HP N54L and DSM4.2-3211 Repack v1.2,
I'm running 5x4TB (WD-RED) in SHR mode, so it took "a while" until the system completed the raid/parity checks.
Using the external monitor program, from Synology Assistent, I saw 100% CPU usage during the diskcheck, so I thought that was the reason.
When Volume1 was declared "healthy", I did a controlled reboot, hoping the problem would go away, but no such luck....
Googled and read some posts, referring to the SNMP service, which was disabled.
Tried to enable and reboot, no change, tried to disable again and a new reboot, no change.
Using putty, I connected and ran "TOP", and was only seeing some 2-3% CPU being used by fileindexd (if I remember correct).
But still the external monitor shows me 100% CPU being used.
(I have tried to look for the Virus/backdoor files that is currently "running around", but have found no trace of it).
Question:
Has anyone else experienced this, and found a way to solve the problem ?
disclaimer: Yes, I know I should have used an UPS, it's on top of my what to buy next list
Edit:
Topic was "Failing resource monitor widget, CPU usage ?", changed to