Thanks a lot for your advice.
The machine was indeed in a bad shape. Everything went haywire since it was upgraded from Win7 to Win10. I tried to "Reset" the OS, with "keep personal files" option (didn't work) and then "don't keep files" option, and none of them work. I had to really format my hard disk to wipe out everything and reinstalled from scratch. That took me couple days because I had to find some place to back up my stuffs.
Then, after the reinstalling win10 from scratch, my network connection was dropped from ~180-200Mbps to abysmal 2Mbps (not a typo)! I upgraded all the proper drivers and couple more trials of reinstalling Win10, but it's still the same. And finally I gave up, I am now switching back to the old trusty Win7. Hotfix updates aren't failing, and the network connection is happily running ~180-200Mbps. Too bad I can't use Win10, but running Win7 is really hassle free for me while Win10 is breaking everywhere.
Although the outcome is not what I expected, I'm still a happy camper now because I can finally not to think about this problem since I upgraded from Win7 to Win10 a year ago. (The problem has been bad for me because it kept rebooting the PC in my bedroom every now and then to wake me up in the middle of the night because it tried to upgrade (and failed))
Thanks very much for your help! I really appreciate it!!!