Want full security at my system.

Dear Friends,
I have home PC and i want to do it full because i am doing very secure work of my company and some competitors want to access our system without our permission and i am feeling risk i want to do it full secure. Can anyone tell me which window is much suitable which software also tell me all methods by using that i can do full secure my system. Only professional person give its answer how have done work in large organization and have strong local and global network knowledge. because your answer can save us and if you give low quality answer then it can create lot of problem for us and we can waste lot of money so i again say only professional and expert person give its answer.
Tell me common software or methods by using that i can go in risk.
Please tell me almost all detail which you think that this should be necessary and this will be dangerous. I hope you will understand all problem.
Thanks
