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.
If it’s possible to update to a 64 bit version of Windows, we recommend to use the lastest GNS3 version if possible. Bugfixes and improved User Experience (UX) are continually being added.
Where I can download the IOU VM?
The IOU VM for GNS3 1.3.13 is available on https://github.com/GNS3/gns3-gui/releases/tag/v1.3.13
If you are looking for an IOU VM release for GNS3 1.4 (or later), was superseded by the GNS3 VM.