It is important to keep your Trading and Demat account active in order to transact whenever you require. Accounts get suspended for any of the following scenarios

1) If there is no trade executed in 24 months 

2) If PAN and Aadhaar are not linked

3) If your Email/Mobile is not validated by KRA

4) If your account is marked not permitted to trade by Exchange for any reason

5) Important KYC Attributes such as mobile, email, address etc., are not provided

6) Based on Regulatory alerts 

You may in such cases, do the needful to provide the relevant data or do a re-KYC here to activate your account.  Check here to know how to re-activate your account.