The GA-EP45T-UD3LR comes with Intel's "Flex Memory technology," which allows the motherboard to react gracefully if multiple RAM types are installed. So this motherboard should not freak out because of differences in RAM, or at a minimum, the Intel Flex should provide you with a message at POST about it.
If I were you I would try removing the old RAM, and installing the new RAM in the same slots. Does the computer boot normally? If so, the new RAM sticks are probably OK.
You also might want to go into the BIOS and load the fail-safe defaults for your DRAM configuration as on page 37 of the manual
http://download.gigabyte.asia/FileList/Manual/mb_manual_ga-ep45t-ud3lr_v1.1_e.pdfAlso - if you're getting beeping at the failed boots, check the beep codes on page 98 of the manual, that might shed some light.