error when building project when executing step 'qmake'

[tarkijowow]

Try executing the steps one by one.
Try first running qmake on the project.
Does it succeed?

do you mean trying to run a simple program? I've done it and it give me the same compile output

[high_flyer]

no, I mean running qmake on the project.
In QtCreator, right click the project and select "Run qmake" or on the console in the folder that contains the *.pro file, run qmake <name>.pro

[tarkijowow]

no, I mean running qmake on the project.
In QtCreator, right click the project and select "Run qmake" or on the console in the folder that contains the *.pro file, run qmake <name>.pro

Yes and this is the output

20:56:39: Running steps for project untitled...
20:56:39: Could not start process "C:\Qt\Qt5.1.1\5.1.1\mingw48_32\bin\qmake.exe" C:\Users\Rizky\Documents\untitled\untitled.pro -r -spec win32-g++ "CONFIG+=debug" "CONFIG+=declarative_debug" "CONFIG+=qml_debug"
Error while building/deploying project untitled (kit: Desktop Qt 5.1.1 MinGW 32bit)
When executing step 'qmake'
20:56:39: Elapsed time: 00:00.

20:56:39: Running steps for project untitled...
20:56:39: Could not start process "C:\Qt\Qt5.1.1\5.1.1\mingw48_32\bin\qmake.exe" C:\Users\Rizky\Documents\untitled\untitled.pro -r -spec win32-g++ "CONFIG+=debug" "CONFIG+=declarative_debug" "CONFIG+=qml_debug"
Error while building/deploying project untitled (kit: Desktop Qt 5.1.1 MinGW 32bit)
When executing step 'qmake'
20:56:39: Elapsed time: 00:00.

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[high_flyer]

Hmm...
Try the following:
1. Rename your *.pro file to *.pro_old
2. in the console, from the root folder of your source run:
qmake -project

This should have create a new *.pro file.
If it did, try simply to call (from the console):
qmake

[tarkijowow]

Hmm...
Try the following:
1. Rename your *.pro file to *.pro_old
2. in the console, from the root folder of your source run:
qmake -project

This should have create a new *.pro file.
If it did, try simply to call (from the console):
qmake

Sorry but where should I actually save the project file?

[high_flyer]

Sorry but where should I actually save the project file?

There where it is now.
At the root of your project source directory.