If a reinstall fails, the issue is almost certainly the C++ runtimes.
Important: Even on a 64-bit version of Windows, Rainmeter may require the x86 (32-bit) version of the C++ redistributable. Make sure both are installed.
Windows uses PATH to find DLLs. If the system PATH is missing the System32 folder or the Visual C++ runtime folders, Error 126 occurs.
In Windows programming, Error 126 (ERROR_MOD_NOT_FOUND) translates to "The specified module could not be found." In Rainmeter's context, the module in question is almost never Rainmeter.dll itself. Instead, it is a dependency of Rainmeter.dll—most commonly, the Microsoft Visual C++ Redistributable runtime libraries.
Think of it this way: Rainmeter is a high-performance car, and the Visual C++ Redistributables are the specific fuel and oil it needs. Error 126 appears when the right fuel is missing or corrupted.
If the DLL file itself is physically missing, a reinstallation is required.