|First of all you should NEVER use water inside the case. |
Overclocking means running the CPU at a higher frequency than the default.
Go to the office supply or the computer shop and buy a can of compressed air. Use it to blow out all the dust/dirt inside the case. This will be messy so you may wish to move the case somewhere else. Be sure to blow out the power supply from both ends.
You may have slightly moved the heat sink/fan assembly when wiping inside. For best results you should remove the heat sink, clean off all old paste or pad and then apply a small amount of thermal paste to the processor as described in the link below.
You don't have to use Artic silver compound. You can buy any generic from Radio Shack or any computer shop.
To answer your question about case fans. First off, the header must be monitored in the BIOS. Second, you must have a 3 pin connector and connect to the motherboard headers.
I wouldn't worry about the other case fans. That said, you should not need 4 case fans.
One 120MM or larger fan mounted high in the rear of the case is all you need in addition to the power supply. I suspect you have a case with side and/or top fans. IMO these are not good for cooling. The fans fight one another. Also, cases with BOTTOM mounted power supplies are less able to cool properly.