Ok it really is a process of elimination, of the top of my head I will list what could be the potentional cause, but you have to do the testing if you need any help with any of them then post what it is you have tried and or stuck with and I or somebody will get back.
jiffz some of it might not be possible for yourself without access to the router/access point but if you do have access or could possibly talk to whoever does and see if they have any issues or possibly even put you in the DMZ that would help.
So from the top of my head this is some of the potential causes.
Main internet connection - you would need to contact your ISP if this is the case have them test and fix the line. I think you can rule this out though as you state you have miltiple computers and only one is causing the problem. So i won't cover this.<<<<< Corection this is the only one having this problume
Wireless access point/router - It could be your wireless access point itself has a fault of some sort, it might be the firmware needs updating or it needs a reboot depending how much traffic you have running through it the logs and routing tables can become full and a reboot from time to time will fix connection problems. Also the channel you are using change it to a different one as you might be getting interference from other signals. If your access point has a built in firewall and you are using NAT then you might need to configure port forwarding for testing the easiest method is using DMZ feature.
Wireless device on the PC - The wireless device on the pc itself might be faulty, try hard wiring the PC to the router and see if the problems still happen. Try different driver versions for the device. Install a new wifi card.
Software - It is possible that some software might be causing the problems such as firewalls or even anti virus and anti spyware software, or a virus/malware. This is a case of running virus checks, disabling testing and even removing the software and testing again.<<< All ready done these still have the prob
I think I have pretty much covered them all if not am sure others will add on other possible causes, if you need help with any of the above then post back, include as much information as you can such as brand and model numbers etc.<<<< For what router or computer?
