If you didn't get recovery discs with your laptop, you can just install the OEM version of Windows 7 (same edition as you have now) and transfer the certificate and token required for OEM activation. I've done this with my Dell laptop, like so:
1) Run "Token Restore" and backup your "token". You'll need to use Google to find this program.
2) Install a fresh OEM version Windows 7 (NOT a retail version) and do NOT enter a serial when asked.
4) Use "OpaTool v0.7" to install the correct "certificate" for your machine (e.g. DELL, SONY, etc.).
5) Use "Token Restore" to restore your backed up "token".
HOWEVER, I've only done this once and if you muck it up (or my instructions are missing a step), it might be a headache to activate your new copy of Windows. I'd suggest doing a bit of research about this first.