ASUS Sabertooth Z87 Boot issue

Do you have ANY kind of an overclock setup or are you using RAM that is listed as supported by the motherboard with an (OC) next to the module specification for the motherboards supported memory speeds? More often than not, this issue is related to the motherboard not liking something about the memory configuration, such as perhaps one of the modules being faulty or using a speed not natively supported.

An unstable overclock, whether from memory or the CPU can cause this as well. In some cases it may be that the motherboard does support the memory speed, but the CPU does not, and so it creates an error by being configured at that speed and the system has to underclock the module to configure compatibility.

What happens is that the computer begins to boot and then realizes something in the configuration is not right, so it changes the setting to something it can live with, resets and continues to boot up. I'd check my BIOS settings against what's actually being reported in windows using a utility like CPU-Z, GPU-Z, HWinfo or HWmonitor to see if there are any inconsistencies in the reported specs. If the RAM is, for example, DDR3-2133mhz, and the motherboards memory support looks like this:

4 x DIMM, Max. 32GB, DDR3 3300(O.C.)/3200(O.C.)/3100(O.C.)/3000(O.C.)/2933(O.C.)/2800(O.C.)/2666(O.C.)/2400(O.C.)/2133(O.C.)/2000(O.C.)/1866(O.C.)/1600/1333 MHz Non-ECC, Un-buffered Memory

it indicates in that specifications listing only DDR3-1600 and DDR3-1333mhz RAM are supported under normal conditions without any advanced configuration by the user or motherboard.

This may not be THE reason for your problem, but it's certainly common enough and might likely be a good place to start looking. If something like this IS going on, you should be able to manually correct the setting in the BIOS so that it boots normally on the first attempt instead of having to make corrections during each boot cycle.

I'd also check to see how much RAM is being reported as present in Windows, since if there is a faulty module it might be reporting a different amount than what is actually installed. You can check this in the BIOS too.