To compile SLEPc (Scalable Library for Eigenvalue Problem Computations) in a Windows environment, you will need to follow these steps:

1. Install a C compiler. You can use a compiler such as GCC (GNU Compiler Collection) or Microsoft Visual C++.
2. Install CMake, a cross-platform build system. You can download CMake from the official website (https://cmake.org/download/) and follow the installation instructions.
3. Download the latest version of SLEPc from the official website (https://slepc.upv.es/download.php) or from the SLEPc GitHub repository (https://github.com/slepc/slepc).
4. Extract the downloaded archive to a directory of your choice.
5. Open CMake GUI and set the source directory to the directory where you extracted SLEPc and the build directory to a separate directory where the generated files will be stored.
6. Click the “Configure” button and select the compiler you installed in step 1.
7. Set the desired options and click the “Configure” button again.
8. Click the “Generate” button to generate the project files.
9. Open the generated project files with your compiler and build the project.

If you are having issues building the SLEPc library, there are a few things you can try to fix the problem:

1. Make sure that you have installed all the required dependencies and that they are compatible with your compiler. SLEPc has several dependencies, including PETSc, BLAS, LAPACK, and MUMPS. You can download these libraries from their official websites or through package managers such as Homebrew (on macOS) or apt-get (on Linux).
2. Check the output of the build process for error messages. These messages can often provide clues as to what is causing the build to fail.
3. Make sure that you have set the correct options in CMake. You can customize the build process by setting various options in CMake, such as the type of build (e.g., Debug or Release), the installation prefix, and the libraries to use.
4. If you are still having issues, you can try building SLEPc from the command line instead of using CMake GUI. This can sometimes help to reveal additional error messages that may not be visible in the GUI.