Could be congestion on your wireless network. Someone may have also hacked your router and put in time-of-day settings to only allow you to connect at specific times.

Check your router settings, and also try a wired connection to see if it changes anything.

is there a possibility that for example your brother or whatever is at home only at the morning?

Same IPs can be conflicting. So try to manually assign a new IP to your laptop (be sure that its not used by any other device.

Cant your laptop see the wireless network?
Can it see it but cant connect?
can you connect but are "blocked" from accessing the internet?
Have you tried whether EVERYTHING is not working or just browsers etc? (sometimes browsers dont work but e.g skype still does etc)

When I use the PC in the morning there's no one else at home.

Yes it can see the network, but it cannot connect. It just tells me that it can not find a stabile connection. I've actually only tested if the internet only works with spotify and google chrome, but I assumed because it's not the browser having troubles, but the Pc connecting, I should have the same problems everywhere else.

My mom's PC had the same problems, and even worse, as when connection was possible, connection was very shaky and fell very often. When her old PC died, I built her a partially new one, replacing only PSU, mobo (with on-board GPU), CPU, CPU fan and RAM, I upgraded her from Win XP to Kubuntu, and I kept the old case and disks and THE OLD Wi-Fi USB key: well, with the new OS and drivers, it works perfectly, it looks like the old XP ones couldn't manage correctly the connection when there were many active connections in the neighbourhood.
So, you could boot your PC with a recent live Linux distro (so you won't have to modify anything installed before having more infos), if the connection will work well, then it's a purely SW problem, the drivers themselves or some conflict between wi-fi drivers and other drivers or other SW.

I have very dextrous toes, but I'm afraid I cannot help you.

Thanks! You guys have been really helpfull. Hopefully I'll get it fixed tomorrow.

@Lemonslice: If we all possesed the necessary information and the uttermost perfect toes at the same time, the world probably would have stagnated.

I've been dealing with flaky wireless on countless PCs and routers from all makes for the last 10 years.

It's nearly impossible to pin down the issues. The only permanent solution is wired.