Windows 7: HDD too small, can't mount without additional kits.

I recently bought a new computer, it came with a 1TB hdd which was mounted. I had a new 1TB HDD already, and when i tried mounting it, it was to small, the HDD that the pc came with had some plastics on it's sides that held it properly.



I mounted the HDD and put it on the Case floor, it's working but recently i've been getting I/O errors, it all solved when i unplugged and plugged it again, but my question is, how do i mount it properly without those plastics as i don't know what they are or how they are called?

That sounds strange.

Well, first of all take a picture of your case and current mounted hdd. That would allow us to see what is the actual problem.

Its very possible that first hdd is 3.5" and second one is may be an 2.5"one. Take a picture of the second hdd as well and post it here too.

Also you should know that bottom of the case is very unacceptable choice for placing such sensitive electronic equipment as hdd! I hope that these errors are because of bad cable contact, but...
You can download this free program CrystalDiskInfo to check parameters how good are they. Take screenshot from it and post it here.