If you use a 32 bit version of Windows, you will need to use GNS3 1.3.13 (or older). 32 bit support was dropped starting with GNS3 1.4.
Download GNS3 v3.0.4 for Windows GNS3 v3.0.4 checksums (February 25, 2025) : File:GNS3-3.0.4-all-in-one.exe SHA256: 6c8910b182b07aeccbe7d3e61296b7183e64f04eda6de15279f5e118166ac9a2 File:GNS3.VM.Hyper-V.3.0.4.zip SHA256: cc4f367dc1cb28dca496d05627e712dad4eb2766f316ca9a7...