For unknown reason, my VPS was shutdown for over one day. At first I thought it's a temporary network issue, so did not take it seriously.
While today I still could not access my website, so I opened the administration panel and found the status was offline. I tried to launched the control panel, but forgot my ID and password. I inputted wrong information over three or four times in a row, then I was blocked.
I had to raise a ticket to the service provider -- HostKvm, and received a email update within 5 minutes, then I opened my ticket and got my new password, while I did not know my ID, so asked they to send the ID to me, and almost got their response just after I updated the ticket. They send me a link and I could open the control panel, then I booted my VPS and it worked well.
I have to say the service speed and quality impressed me deeply, and I want to express my deep appreciation to them here!