@MisterMac: Mounting an HSF means inserting the 4 rubber pins into the holes on the motherboard, pushing 2 at once (diagonally) and turning the rubber screws using a screwdriver right?
The PC came with thermal paste which i cleaned off and applied once again. the thermal paste i used was Thermaltake TG2.
HSF
The Intel processor installation guide has warnings everywhere that it needs to be installed by a professional, and seeing so many problems related to just wrong HSF installation, its very true. People either decide to skim over it or merely choose not to read it at all, thinking they are perfectly capable.
Not saying you, or any other people with such problems are stupid or anything. It really helps to learn properly.
Here's the page for LGA1155 installation guide:
http://www.intel.com/support/processors/corei7/sb/CS-032070.htm
Read the page throughly, then do the installation. The thing to note is if the plastic fastener broke off because of wrong installation, then you'd need to buy a new HSF.
The most common confusion seems to be not putting the fasteners in right place before installation.
-The arrow on the fastener points to counter-clockwise turning to
unfasten the HSF. Now if you decide to install the HSF like that, not only it'll be loose, but you will damage the mechanism
-Check that the plastic fastener is flush with the motherboard. Check all 4 sides. If you decide to install the CPU on the motherboard before putting it into the case, you can even check the back side of the motherboard.
About the thermal paste: I've removed the HSF and CPU 2-3 times for the 2600K system on my sig, not bothering to re-apply the TIM. It seems installing the HSF properly is a priority to proper TIM application, although both are important.
Memory
I could have saved $20 and got memory that required 1.7V to work at manufacturer settings. I decided not to do it and paid a little more. Since I'm using the same memory I used for my i5-661 CPU, it was a while ago and memory was much more expensive. DDR3 at even 1.65V(the maximum the motherboard supported) wasn't so commonplace.
I'm not running the memory at its full speed, but even at full speed requiring 1.65V, it would be just at the maximum level stated by chips that use integrated memory controllers(Nehalem and later).
Now, 1.65V is an absolute maximum level. You don't want to go any higher than that.