Thank you for all the efforts you provided to me, I'll have to read a couple of more times to understand all these procedures. Here is another piece information which may help. The very first time when I had the boot problem, the system put out a message said 'Your PC has problem...' then went into automatic repairs, and said 'this repair process... may take more than an hour......', But I let it run for 10 hours, it just keep running, never ends, so I had to power the PC off. It did that twice, after those 2 times, the third time I boot, I don't get automatic repairs anymore, but got that 0xc00000f error code, from this error screen I can only retry or go to UEFI(BIOS). I did try F2,F8,F10,F12and Shift keys, all I can get is UEFI screen, never reach Windows. May be I did not tap the key fast enough, I'll try them again. Early Today, I used Windows 7 recovery disc ( I created from my Windows 7 PC, and I know this disc works because I used it once to recovery my Windows 7 PC) to boot, it load the windows 7 and start to recovery, ask me which language, etc.. but stop at the screen to choose either factory recovery or system file recovery, said can not access the HDD, I/O error, ........ Well, this information may or may not help, but I'll try the steps you provided.. I also ordered a new HDD, should be here in a couple of days. Thanks again for all your help. ------- I Just don't understand, why this HDD has access problem or I/O error on the Dell Windows 8 PC. but I can access this HDD as an external disc on my Windows 7 PC (Its a Acer PC) without any problem(except DSKCHK). Wonder if I can try to boot the Acer PC from this external HDD ?