It says if you report your PC as defective in the first 7 days you can get a return and refund or a return and replace.
The distance selling regulations permit you to return for refund within seven days for ANY reason.
The sale of goods act permits you to return for refund after any reasonable period of time, if the goods are not as described, of merchantable quality, fit for purpose, etc.
Personally, I wouldn't give them the option of telling you how to fix it. If you let them do that, you lose your legal right to a refund, and you're left trusting them to do the right thing. Something they demonstrably haven't done to this point. They clearly knew it wasn't working and sent it out anyway.