Ebay do allow sellers to sell laptop repair services on the site, but they should be listed using the classified ad. format, and are not covered by the Money Back Guarantee.
Most of the laptop repair services I could see don't use the right format, but advertise a service as if it was a tangible item.
However, after 30 days, even if the service you used was incorrectly listed and shows as covered by the MBG, after this length of time, there is no way to make a claim through Ebay.
Personally, I would write to the person involved, telling them what you expect them to do and giving a deadline.
If there is no reponse to your letter, you may have to consider taking legal action, at the very least so you can get your laptop back and take it elsewhere.
Citizens Advice may have further suggestions but they do usually advise making contact as a first step.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)
