Something wrong with my brakes I bought a new bike with hydraulic brakes in september 2019. It was working fine for a few weeks but after that I started to notice my disks blackening and the brakes lacking power.I got told that there was probably air in the system so went to the shop to get it fixed which they did for free as it hadn't been over 6 weeks since the purchase.This is a link to the old thread which helped me a lot but I haven't had a chance to visit the shop due to bad weather. Hydro brake disk blackening
It's been about 2 to 3 months since that thread and the weather finally settled this weekend so I took my bike out only to find that none of my brakes work at all now.Im not sure what to do now.Id be grateful if anyone can help.BTW they are Clarkes brakes
Black stripes on the disks usually means contamination. Disks should look shiny and clean.

This could have been picked up from the road e.g a splash of oil or diesel, or the callipers are borked and leaking fluid or oil depending on what Clarkes use. 

Take the callipers off the bike and examine them. They will be dirty but shouldn’t look “wet” behind the pad or near the bleed valve or anywhere really. That would be a sign that they are leaking. If they are leaking they need to be fixed or replaced. 

You need to decontaminate the disk by removing it from the wheel, sanding lightly with very fine grade sandpaper on a flat surface and cleaning with isopropyl alcohol. You can get the isopropyl from a car supplies store very cheap. It’s called brake cleaner. 

The pads might be able to be decontaminated by cleaning  with isopropyl and sanding lightly. More extreme is setting them on fire (outside) with the alcohol and again cleaning/sanding but also likely is that you need a new set of pads. Organic pads soak up contaminants and emit them like a sponge. 

You can tell if your brake lines have air in them if the levers are spongy/springy when you pull them hard. The bite point should be relatively hard in air free lines. Do this with the wheels installed, don’t pull your brake levers when there’s no discs between the callipers. 

All these cleaning things are super easy to do at home with a hex wrench and screwdriver. There are many good YouTube videos on the topic. GMBN has a good one on decontaminating disk brakes.