That is definitely not the case... many of us have been running multiple instances under Windows for years.
F12 to open it and include any errors you see. If this is not working in IE, then I'm not surprised... most of us use Chrome because D3 running in IE is problematic.
In order for us to help you further without having to guess, please include the following information:
- nodejs version
- npm version
- node-red version
All of these things (and more) can be found in the node-red log when it starts up. When you paste that output here, please put it into a code block to make it easier to read -- just put a separate line with 3 backtics
``` before and after your log output.