how to run apple hardware test with no cdrom?

My MacBook Air won't recognise old or new hard drive and I believe I may have a logic board issue. My external CDROM has also just stopped working due to the wire being split some. I have two questions, can I get a replacement wire for the CDROM and can I run Mac hardware test on my 2008 MacBook Air without a CDROM? I still have the original CD1. I am currently booting the mac from a Lion installation on an external HDD attached to the USB port.

If the answer to those is no, where can I sell this stuff for scrap? 😟

Thanks