How important is the hash power in solving a block? What is the role of hash power in solving a black, I have read at numerous place it's more like a lottery to successfully form a block in bitcoin and any such crypto blockchain currencies. 

Is it importance of hash power or luck that plays the role? If it's all about hash power then why is so, that people with huge hashes at time fail to achieve blocks but little ones get them? How much is real computation power involved along side fortune factor?
Hash power is like a lottery ticket. The more you buy the greater the chance you have that one of your tickets will match the drawn numbers. 

But a person with one ticket can also win just the same. Each ticket has the same chance. 

Having a higher hashrate simply gives you more chances to win within a given block frame. 

In the end it boils down to luck. But the more attempts/lotto tickets/hashpower means your odds of finally matching/winning/solving increase.