uefi can be problematic as is evident in any search on the matter including older versions of windows however many have success with a little determination.
understanding your hardware is very important and understanding uefi is equally important prior to attempting an install
There is a link on uefi and slackware near the top of roarde's link that is worth the read.
here are some additional links that may prove of valuehttp://www.rodsbooks.com/linux-uefi/https://wiki.archlinux.org/index.php/Unified_Extensible_Firmware_Interfacehttps://help.ubuntu.com/community/UEFIBooting
As this is a new motherboard insure that your ram is seated well and check cables and insure clean partitions appropriate to the install.
You will most likely require legacy mode, as you say it is legacy + uefi, so you may need to use the info regarding creating partitions and boot setups for uefi
If you become frustrated with attempts to install slackware or Vector take a break and try mint, ubuntu or fedora as they are likely to be more frequently tested and developed on various uefi/secureboot situations. This may allow default mode installs as ubuntu added keys in some distros to allow dual boot with window
testing alternatives may assist in undersanding the issues involved. If you purchased the board new you may still be able to return it for a gigabite or asus board that has more wide spread usage in the linux community. those with a toggle for legacy bios should allow a standard install, legacy + uefi may not be a legacy bios and thus require additional steps
assistance in this situation requires clear communication, Be as specific as possible when posting further attempts and error messages.
Best of luck