Is the 2 8 pins ATX 12V connectors that is on the motherboard has too be connected in order to sufficiently power my i7-2600s CPU? My power supply only got 2 4 pins ATX 12V connections, so I can combine them to connect to 1 8pins ATX 12V connector only, will this work? Please advice....Thanks.

Welcome to the forums..The dual 4-pin (4+4) ATX_12V connector from your PSU is actually just one 8-pin ATX_12V connector split in half for compatibilty reasons for various different motherboards..So yes, you would combine the dual 4-pin (4+4) ATX_12V connectors from your PSU to make one 8-pin ATX_12V connector that goes into either of the motherboard's two 8-pin ATX_12V power sockets..It will fit, that's the way it's designed, and should work just fine..Like Gamerx said, the second 8-pin ATX_12V would only be necessary if the CPU needs the extra power for stability when extreme overclocking..Read here.
 
If you run into stability issues that would require extra power from the other 8-pin ATX_12V, you would need to try an 8-pin Y splitter or a molex to 8-pin adapter, or get a PSU with the neccessary connectors.