please help me ! how to protect my computer

My company (http://www.cnmoulding.com/) is engaged in production of molds and related OEM orders for
factories.
    Yesterday, I was shocked to encounter a thing, and I was even able to steal e-mail client,
misappropriation of my name to my customer fraud,
 The con artist but there are still my personal e-signature document.
     I want to please help me, how to prevent this crime?
   Where should report, I have a friend to lie to the Australian 2 million, said Hong Kong
Commercial Crime Bureau report, may be that effects are not.
   The following are the criminals to my client's payment account
 Bank Information:
 Name: HANG SENG BANK LIMITED
  Address: 83 DES VOEUX ROAD CENTRAL HONG KONG
  A / C holder's name: GUANGBEN TECHNOLOGY CO.LIMITED
 Account No. (A / C No.): 274-369818-883
 SWIFT CODE: HASEHKHH
 WESTERN UNION INFO:
 NAME: JIAONI YANG
 COUNTRY: SHANGHAI CHINA
 Please help me out of ideas