There are plenty of places around NW London that claim to be bale to fix PC's but not sure how good any of them are. But first things first. You never know we might be able to sort you out on this forum. So, what do you THINK is wrong with your PC and what steps, if any, have you tried to resolve your problem? What operating system are you using and what other software have you installed? Have you done anything particular just before you first noticed that something was wrong? What devices do you have attached to the PC and have you treid using you PC without any of these attached?
OnePlus 5 review