I flashed Samsung Galaxy S and now it won't start beyond logo screen I was trying to install Cyanogenmod and after the step in which I went into download mode and moved mod to SD card and do "hermidal zimage" which opened up Hermidal in which everything was successful; no errors and stuff. 

Now about Zimage to be renamed recovery.img...that step I didn't do. Because that made no sense; first in the guide it said rename it if you are a Windows user but later on it says to use a file named that, so I had to rename it to the original. But I don't think this is the problem.

I can't get into recovery mode, or start it normally. What I can do is go in download mode. 

Whenever I start it, it just shows a big "S" and  the Samsung logo and stays stuck at that boot screen.

It keeps flashing and then just stops flashing but after that the boot logo stays there.
If, as you say, you can get into download mode (Odin), then you can use the Odin desktop app to re-flash the stock firmware. I encountered the same symptoms multiple times for different reasons, and re-flashing the stock firmware fixed it.
The process is a bit tedious but not too complicated:

Download and install the Odin desktop app.

Obtain the firmware files. You can get them from samfirmware.com. For most Galaxy S4 models you can find them through GalaxyS4Root.com, which I find quicker. (You don't need an account to download, you just need to solve the advertising Captcha at the bottom.)

Boot your device to Odin mode by holding the volume down button, menu button, and power button. Add the power button to the combination last, and hold for a few seconds, until you see the warning that says A custom OS can cause critical problems..., then press the volume up button, which should bring up a screen that says Downloading...Do not turn off target!:


Connect the device to the computer with a USB cable. The Odin app on the computer should print the message Added!! in the message area in the lower left corner.

Click the PDA button, and browse to the firmware file with an .md5 extension (you may need to unzip the file you downloaded in step 2). Odin will go through a verification process. If you get an error message about a version mismatch, that means your .md5 file is for the wrong build number. The filename should include the build number (e.g. I545VRUNFNC5). If you don't know the build number—and obviously can't find out because you can't boot the device—just try all the firmware files available for your model.

Click Start. On the device, you should see some messages in red text (START followed by some numbers in brackets), and a blue progress bar. Wait for the process to complete and restart the device.


Be very careful to make sure the process is not interrupted!. If that happens, you can brick the phone (and I mean truly brick it; it's only soft-bricked at this point). Use a computer that's plugged into a power source, make sure your USB connection is not loose, and walk away from the general area until it's finished. Maybe leave the house and take a drive somewhere to make sure the vibrations of your footsteps don't disturb the connection. If that sounds exaggerated, that may be because I'm going through the pain of an interrupted firmware flash as I type this. ;)