Windows 7 Lagging, CPU Usage Up and Down

Problem and Troubleshooting

Yesterday, my lovely computer running on Windows 7 acted very strange. I noticed that hard drive led indicator turns on and off in persistently since booting. I felt there must be something wrong. After the desktop completely loaded, longer time than usual, the effect became more clear. Mouse move, page scrolling was lagging. My first assumption, it was infected by virus. So I scan with installed AVG antivirus and Windows Defender. The scanning itself took a really long time, and no virus found.

My assumption then changed. If the two antivirus found nothing, the problem must be something else, it could be a hardware issue :( As usual, to identify any problem, I went to Event Viewer. In the Event Logs - System, there were hundreds of error messages saying "The device, \Device\Harddisk0\DR0, has a bad block." OMG and bingo!

Immediately I ran scandisk for all partition in the hard drive and restart the computer. Scandisk usually will solve "light" hard drive errors. Unfortunately, even after scanning twice, I was not lucky. The problem was intact.

Solution

So, Google help me finding some forum with people having some problem. It seems likely that my hard disk got bad sector or similar. People in a forum suggest to scan with hard disk diagnostic tool, provided by hard disk manufacture. Since my hard disk is Seagate ST3500418AS, so the diagnostic tool must be available in Seagate web page. Short story, Seagate has a diagnostic tool called SeaTools. For Windows, there are two versions; DOS mode and Windows mode. The tool is packed in bootable CD image, so you need to burn it to blank CD. Since I didn't have any blank CD, luckily I found a way to install SeaTools to USB flash drive.
Google "install seatools on usb" to find a bundle of SeaTools image and utility to make a bootable USB. The instruction how to install SeaTools on USB usually available at the web sharing it.

Short story (again), before running SeaTools from the USB, I have to make backup of the broken hard drive just in case SeaTools can cause data lost. Although I didn't backup all the data, the backup process took a half day with hard disk in such condition. I also suggest you strongly to make backup of your data first.

After backup, it's time for SeaTools to work. Insert the bootable USB drive, SeaTools will loading, select the target drive and do Basic test. If basic test fail, go with Long test. On my 500 GB drive, it took around one and half hour to complete scanning and 2 errors found. The repairing process itself  ran "semi automatically", just click repair, Ok, etc. After finally the scanning and repairing finished, I restarted the computer, and the problem had gone. yay!

TL;DR

CPU usage up and down, computer lagging it turns out a hard drive problem. Install a hard drive diagnostic tool to USB drive, make backup of data, run the diagnostic tool. Problem solved.