It depends a lot on which service you use to get onto the internet.
Do you use a normal telephone landline (BT or another supplier) with a dial-up connection or do you have broadband? Does your internet signal come via satellite through a dish on your house or do you share the satellite signal with other local properties?
With a dial-up connection you cannot get onto the internet while you're using the phone to talk to someone. If you can do both, then you have broadband.
The first people to talk to would be the company that provides your internet service or ISP.
They will want to know what operating system you're using; which modem you have.
There will be many other questions which will depend on your personal computer setup.
It can help if you have an idea of what speed of service you expected as stated in your contract with your ISP (it's never as high as they say) and what you are actually getting when you do get on line. This link provides a useful tool and will build up a set of graphs for you to compare at different times of the day and over several days.
http://www.mybroadbandspeed.co.uk/ . If things go too slowly you can get error messages because the system thinks you (the computer) has given up and you can drop off line. If the bandwidth available on the internet is too small at any time, even your meagre input is too much for it. Your location throws up a few warning signals for me so your ISP is the first port of call for you really. Good luck.