tl-wr741nd step-by-step Unbrick with serial cabel and tftp

First of all, my router was hanging on the start, it started and stopped when all the leds were lighting.

To connect the router to the pc via serial cabel you have will need a cabel like you can find on this page:
http://wiki.openwrt.org/doc/hardware/port.serial.cables
(You can see the connectors as well)

Now you should connect the wires to the router motherboard. You can find the connection points by searching on openwrt wiki. For wr741nd http://wiki.openwrt.org/toh/tp-link/tl-wr741nd

If u connected it to the router and the router to the pc with it you will need a program to connect via serial port.
I used putty for it on Windows.

Start putty and select serial on the main page at the midle of the right side.

To know which com port do you need right click on Computer-> choose Manage-> choose Device Manager-> Choose Ports and open it.
Now you will see the name of the device and at the end the COMX where X is the number.

So if u get the COM port number go back to putty and write it into the serial line and the speed which can be found on your routers page. For wr741nd on my pc looks like: Serial line: COM1 Speed: 115200.

If you click to Open on the bottam you will get a black blank window, now you should restart your router while the window is open and the router is connected to your pc by the serial cable.

As i noticed while i was searching on the internet if you see the Autoboot in 1 sec (or something like that) the router works well, you can continue the working with it, is you dont get it PLEASE ASK ABOUT IT ON THE FORUM AND POST THE FULL LOG OF YOUR WINDOW by select it with the mouse and copy paste it with ctrl-c, ctrl-v.

To get acces to your router command line you should be fast and if you see the Autoboot in 1 sec as fast as you can type in "tpl" without "". If you did it well you will get something to the beginind of the line which indicate you are in the command line.

Setup the tftp.

You will need an cat 5 UTP cable to connect the router to the pc with one of the lanports.
Next step is configure your network to ip: 192.168.1.100 Subnet mask 255.255.255.0 and Default getway 192.168.1.1
(The ip adress what need to you can be different and can be found on your routers openwrt page)

For the server you have to download and install/run the tftp32 program:
http://tftpd32.jounin.net/tftpd32_download.html

Set the tftp directory: tftp32->Settings->TFTP->Base directory->browse (select the directori where the firmware is located)

To be everything well please turn off your firewall or add the program to the exceptions.

You are done with setup the server.

(Most Risky Part If You Dont Know Anything Dont Do It)
Now you have to go back to the putty serial screen with command line.

The following steps can be found on your routers page, if you cant find them ask on the forum.
THE NUMBERS IN THE STEPS ONLY FOR THIS FILE AND THIS ROUTER EVERY TIME CHECK THESE FOR YOUR ROUTER AND FILE.

1st: get the size of your file in hexadecimal instead of decimal.
right click on file->proper->size in bites
Now start calculator or any converter and convert this decimal to hexadecimal like me: 3932160->3C0000

2nd: type it into the command line: erase 0x9f020000 +0x3C0000
3th: type it into the command line: tftpboot 0x80000000 backup.bin (the file name can be different depend on what did you downloaded or is it renamed or not)
4th: type it into the command line: cp.b 0x80000000 0x9f020000 0x3C0000

5th: type it into the command line: bootm 0x9f020000


To everything be clear i tell you what command do what.

1st get the filesize in hex
2nd you clean the flash memory
3th uploading the file into the memory of your router called backup.bin from your computer. It can take several time, you will see many #### which indicate it is doing something
4th copy the image file you just uploaded from the memory to the flash
5th if everything was successfull it will reboot the router with the newly updated firmware image.

Sorry if i did any mistake in the text, my english not as perfect as i want it...
I writen this step-by-step because i like this type of tutorial, these are easy to follow dont have to think about what sould be happend here or the other how did get XY screen in their sample posts. I cant find tutorials like this only many small one which had mixed to make it to work for me. I hope it will be helpful for many people who did the firmwre upgrade wrong like me.