You should have received an email explaining the problem and what needs to happen before your account can be reinstated. If you can't find it, click My eBay at the top of the page. You'll find a copy of the email after clicking the Messages tab.
There are two reasons why an account may be suspended:
Non-payment of eBay fees: Account balances of $1 or more must be paid in full each month. We'll automatically reinstate your account once your balance is paid. You can pay by credit or debit card, by check, or through your PayPal account.
Violation of our rules and policies: For policy violations, you need to check the email we sent you. It will explain what the problem was and what needs to happen before the account can be reinstated. You can learn about our policies.