Here are some questions that will help you troubleshoot and solve your situation.

Logs were lost when? Database open or closed? What is a cold backup? Are online redo logs copied for a cold backup? If you think not, then why do you need the current ones? If you think so, how can you recover a database using commands that involve manipulating redo logs? How do you make new online redo logs?

http://tahiti.oracle.com
Do a search on backup, cold backup