I always have used a wired connection to my modem with an ethernet cable but lately when I used it it said i was connected to the wifi router but was still getting 0 internet access. I switched over to using a wireless adapter on my PC and i will have internet for a few minutes to an hour and then it will star to PERIODICALLY cut me off from internet. I know it isnt my internet or SERVICE provider because on my SMARTPHONES and tablets I get flawless internet access. Check that the USB port the wifi adapter is plugged into is not set to turn off after a certain period of time.

To troubleshoot your wired connection that used to work: a) move the cable to a DIFFERENT port on the router (ports do go bad) and b) try a new cable (ethernet CABLES go bad too).Wifi router does it in every one. I'd like to resolve this without spending money.gh12345,
Information you gave suggest that your main computer is having trouble. You need to give details about your computer. Make, Model and age. And whaich operating system.
Have you recently added any new programs?
A new game? A new program to optimize the computer?
Have you recently added new eternal devices? Such as a new printer?
Have you changed the about of memory?

Sometimes failures are not apparent by symptoms alone. A bad power supply could cause some parts of the computer to fail. That s rare, but does happen.
Since the smartphone and tablets are able to connect wirelessly, it isn't your router.
You tried every port in the router and none worked. It would be extremely rare for all 4 ports to go bad.

I don't see how you can avoid spending money to troubleshoot this issue
The cheapest solution, buy a new CAT cable. (or borrow one from a friend to test)
https://www.monoprice.com/product?c_id=102&cp_id=10208&cs_id=1020805&p_id=9548&seq=1&format=2
http://www.walmart.com/ip/Link-Depot-5-Ethernet-Enhanced-CAT6-Networking-Cable-Black/15074921

If the new or borrowed cable gives the same results, then your ethernet/NIC card could be going bad. Then you could either open up the pc and install a new card or buy a USB to ethernet adapter.
http://www.newegg.com/Product/Product.aspx?Item=N82E16833704073
http://www.newegg.com/Product/Product.aspx?Item=9SIAAUJ41K8611

Of course, you if you have trouble with the USB to wifi adapter, you might have to look at the power to the USB ports.
If the wifi works off and on, then a USB to ethernet adapter could have the same issues.