Based on the information you have included in your question, it's not possible to provide a reasonably definitive answer. You're clearly in the early stages of troubleshooting a problem that could have a broad number of possible solutions.
In order to make your question fit the Q&A format of Super User, you must include more information. Here are some suggestions to get you started:
- Make/model of your wireless card and laptop
- Details about the wireless driver
- Output of
ipconfig /all when you do, and do not have connectivity
- Any relevant entries from the Windows Event Logs
- Describe what happened between the last time it worked and when it stopped working
Do your best to use good formatting to make your question easier to read, and be as concise as possible with what you include to avoid going the other direction by creating a question too long to keep folks' interest.
All this said, your question by nature is a troubleshooting question. Such questions, even with adequate details, tend to require back-and-fourth "try this and report back" discussion, which is more suitable for a forum than Super User. So while you may get lucky if someone recognizes your problem as common, be prepared for the possibility it still cannot be answered definitely.