You are not like that alone. Believe that facing a big problem are going to make you big and able to face even larger problem in the future.
Thinkpositive that you are a great man. Remember when you are a baby, you even could not walk, but you tried and you failed, but then you tried again and again then you fell then finally you are able to walk. Finally you can run and you were becoming a teenager.
You cannot die because of your problem. You can do ot.
If you don't like your topic, believe me, what you need is not the topic. What you need is the ability to finish an impossible and unwanted mission. That is the outcome ypu need as a PhD later.
Think that you are special, think that how many percent PhD or PhD student in this world? I think it is only 1 percent even less than 1 percent. So, you are above average and you are not stupid.
I have a friend which was very struggle, even his supervisor changed 5 times but he can manage it until finish the PhD.
My suggestion is you should be optimistic and never compare your progress and work with other PhD student. Every PhD student has his own journey, has different problem, etc.
The most important is you make a progress every day, even it is may be below your prediction.

Allow me to add an advice from religiousperspective , if you are convenient, since nobody give this to you:

If you believe with God, it is the time to activate your emotion bumper: we believe our task as a human only working as hard as we can (we call it ikhtiyar), and the result is not our concern, the result is God's concern (we call it as tawakkal). If you have this kind of believe, you can keep optimist even you are in your top stress level, since you have a Great God, so even the problem is big in your eye, the problem is small in front of the Great God.

Just buy a secondhand laptop on ebay. Find a spec with core i7 and minimum 8gb ddr ram. You just need to spend less than £200 and get a robust laptop.
If you have more money, I suggest to spend on ultrabook with screen at least 12 inch. The weight of ultrabook is so light. Find new ultrabook with minimim core i5 and 4gb ddr ram.