Strange PC "Problem"

Today I decided I would clean my heatsink (Hyper 212 Evo) and obviously to clean it properly you have to remove the screws, upon doing that I decided to try out my new thermal paste, cleaned the cpu, cleaned the heatsink, applied new thermal paste.

I then turned on my PC and the computer was stuck at the BIOS Splash Screen, I was very confused, initially I thought the worst and thought it was my CPU but before I was going to check I wanted to see if it was anything else. I took out my BIOS battery and put it back in and restarted my PC same problem however I decided to press CTRL + ALT + DEL, which just kinda "refreshed" the screen (First time I done this so keep in mind I don't know what it does) and then I pressed DEL and somehow I entered the BIOS? What did I do? However the problem seems to be still there however restarting my PC multiple times and CTRL + ALT + DEL seems to work allowing me to enter the BIOS and the Boot Menu. 

Very strange problem, hope you can tell me what it might be, as it's a problem to work with and obviously I'd rather have the problem got rid of, thanks.

Do not know what the original problem was but regarding CTRL + ALT + DEL  Delete let you enter the bios. The other stuff (ctrl and/or alt) did nothing. Since you removed the battery you probably have to reassign the defaults in the bios before the computer will function properly. Make sure the bios defaults are set plus any custom settings you may have had and save before leaving the bios. See if that helps.

Also make sure you got the heatsink seated properly plus fan plugged in and that you did not damage the motherboard or knocked a cable loose.

Well there's defiantly something wrong however it works now at all times, I just have to wait at the splash screen for 25 seconds until it boots/enter bios. Not amazing, but it's viable.