Windows 7 boots slowly with black screen after "Welcome"

Its just one diagnostic, but it could tell you the cause, or at least eliminate one possibility.

Download and run your hard drive manufacturer's drive tester software tool.  This tool tests the hardware of the drive, which is different from the integrity of the data on the drive that chkdsk does.

If you will provide your hard drive model number, I can provide a link to the appropriate software.

I don't really understand "run hard drive's tester".

Asus don't have tool like this or at least for my model. Or you mean the manufacture of hard drive : WDC WD5000LPVT-80G33 SCSI Disk Device ? I dont think they have that tool

The tool I am talking about is provided by the manufacturer of the hard drive, which is Western Digital.

Go to this place to download the tool

http://support.wdc.com/downloads.aspx?lang=en

It is called Data Lifeguard.  Run all three tests:  SMART, Short and Long.

If any one of those tests fails, it means your hard drive is failing and it should be replaced immediately before you lose your data.

FYI, this is a very good diagnostic tool.  It is provided by WDC to enable people to test their drives when under warranty to prove a warranty claim.  It is also a very useful tool to determine if you need to replace, regardless of warranty coverage.   I have used this many times to discover an underlying problem.

I dont see Short and long settings, but SMART passed.

As I said, there might be no hardware problem, because the same windows 7 homepremium, in the same laptop, still boots fast. I think the problem is in the boot log file.

Good.  That means you can move forward with the knowledge your drive is still good.

If this was my system:

1. I would be most suspicious of malware, run ADWcleaner and have a good antivirus program https://toolslib.net/downloads/viewdownload/1-adwcleaner/

2. I would remove all programs that claim to make your computer run better, safer or faster.  The vast majority of these are in fact malware

3. I would remove any and all "protection" software on your computer and leave just one high quality Antivirus product -- More below...

4. I would be using my hard drive manufacturer's drive testing program to ensure it is not failing

5. I would want to be certain that none of the hard drives are more than 75% in use

6. I would check my memory using Windows 7's memory checker

7. I would install and run Autoruns to check to see what is in the start up process

8. AND, most importantly, take a close look at the applications installed.  Some of them are notorious resource pigs that insist on running on startup.

9. I would remove programs/applications from startup unless I actually need them to startup

   Common miscreants that cause slow start ups:

• Garmin Express

• Roxio anything

• Skype

• uTorrent

• Frostwire

• Trusteer

• Dropbox

• Onenote

• Evernote

• All Apple products

• Quickbooks

• Spotify

• Pandora

• AOL desktop

• Some games, particularly online ones

Thanks for your very detail suggestions. Most of your suggestions I have tried. However, it seems no different :(

Waiting for another idea.

All right! After some days now I decide to finish this problem. I tried to use all suggestions I got, like remove startup programs, scan for virus and malware, run defragment for disk, the problem hadn't gone. I just realized that experts said people shouldn't use registry cleanup tools because deleting some registry values can cause serious problems that can only be fixed by re-install the OS. Some months ago, I used to run those tools. The OS that I don't use registry cleanup tool still works well. 

So, for people who have this kind of problem, don't use any registry cleanup tools if you aren't sure what they delete. Install a fresh Windows with Easy Transfer is a good way to keep your data and make your OS fast again!

Thank you Tung for that feedback. It is rare for people to admit they caused the problem.  You are absolutely correct.  Fooling with the registry is the kind of thing that you want to leave to others.  Frankly, I myself am fairly expert and I have never used registry cleanup tools.

Good solution to rebuild your system.  Would you like some detailed instructions on how to do that successfully?