The only other thing that comes to mind – again, according to your general description – is the following scenario:
- The UEFI Compatibility Support Module (CSM), otherwise known as “Legacy Mode” is activated in your BIOS.
- Manjaro or Windows has been installed with an MSDOS (MBR) partitioning scheme rather than GUID Partitioning (GPT).
In that possible scenario, Windows might begin to boot, but then force a subsequent reboot to allow legacy booting technology to boot next. This is highly inconvenient, and generally not a recommended state.
If this is the case, the only resolve I’m aware of is to install the OS (the OS that boot as legacy) again, making sure to have both OS booting a pure UEFI.
Please provide your system information as described (below).
Regards.
Welcome to the Manjaro community
As a new or infrequent forum user, please take some time to familiarise yourself with Forum requirements, and the many ways to use the forum to your benefit.
To that end, links are provided (below) - Please use them.
Be prepared to provide outputs from various commands when asked. It’s equally important to provide as much actionable information as possible in your first post, rather than simply indicating there is a problem.
Waiting for others to blindly ask questions can be counter-productive – typically, nobody has a 
at their disposal – Instead, please help others to make informed suggestions, based on information you provide.
Update Announcements
The Update Announcements contain important information and a Known Issues and Solutions section that should generally be checked before posting a request for support.
System Information
While information from *-fetch type apps might be fine for someone wishing to buy your computer, for Support purposes it’s better to ask your system directly; 
Output of the inxi command (with appropriate parameters, and formatted according to forum guidelines) will generate information useful for those wishing to help:
inxi --filter --verbosity=8
or the short form (preferred):
inxi -zv8
- inxi man pages (Arch Manual)