Strange behaviour

Yesterday i had a strange glitch with the PC i was playing a game and it just froze, nothing i did could get me out of it i tried everything but to no avail so i held the re-start button down untill it shut off.
When i restarted it would not boot so i pressed re-start once again and all was OK, now at first i thought the GPU had overheated but mine has always run hot around 85 and never had this before.
The rest of the day went OK with no problems, I shut down at night in the approved fashion and forgot about it.
This morning i fired up and i saw the motherboard screen as normal then it started to boot but just stopped with just a small whit square at the top left of the black screen blinking as though it needed time to think so i left it alon for a while but it went no further.
I re-booted and got just the same so on the next re-boot i went into the bios, my PC has always been set to boot from the CD/DVD drive and if it's empty got to the HDD so i changed to boot from the HDD first but still no success, i then re-booted but went via F8 and used "last known good configuration" it then booted OK and has run perfectly all day.

Anyone got an idea what that is ??
thanks

 

Is it a HP or HP product? They have this problem at times.