Windows boot issues- Complicated for me but probably a simple issue for experts

Basically I have an ASUS P6T motherboard with windows 10 on  SANDISK SDD. Every time I start the PC it just takes ages at the bios screen waiting for me to press DEL to go into Bios settings. If I just go into bios and then quickly press F10 and do save & exit, it restarts but this time doesnt wait ages at the Bios screen. However now it can behve in one of the three ways- 1. goes into blue screen where it says could not start after multiple attempts so choose one of the below and then lists 1-9 options. Option 4 is safe mode and if I enter that and then promptly restart then it magically behaves perfectly and works normally.  2. Is stuck at Windows logo with circling dots for a variable period of time after which the dots just freeze at one point or the screen goes blank completely with no option but to force restart by pressing the power button for 5 seconds. 3. Starts normally once in a blue moon. 

I started leaving it in sleep mode just to avoid that but then the other day it would not wake up from sleep mode so it isnt a long term solution.

I have run tests for hard drives, RAM, CPU and GPU but cant seem to find any fault. The power supply also seems to be working ok. Its Crossair TX750M. GPU is NVIDIA GEFORCE GTX 285 (enough for me, I'm not a gamer) . It was clogged up and overheating. I cleaned it thoroughly with new Arctic MX-6 paste and since then the error of freezing of dots under the windows logo is gone, but now the screen still just goes blank at that stage.

I wondered if it was low on memory ( 2gb x 4 Geil DDR3, PC3-12800 ) so I upped it to crossair vengeance 4gb x 3 of  PC3-16000 (in slots DIMM A1, B1 &C1) and 4GB X 3 of PC3-17000 (in slots DIMM A2,B2,C2). Still the problem continued so I tried on 4gb x 3 of one set only at a time. No luck. 

To rule out problem with the Sandisk DRIVE, I cloned the disk to a new Samsung 2tb QVO but I still get the same problem. 

I suspect it is some software issue. Would appriciate any help to make it a bit more reliable. Otherwise I might have to discard it for a more reliable machine. 

kind regards

Ansh Singh