Okey, so this happened to me a few days ago, i can hear sound coming from games and skype but not from my browser. Also sometimes when i unplug and plugin my headphones there is sound but only for a few minutes.
1. Are you using Internet Explorer or any other browser to go online?
2. Did you make any changes prior to the issue?
Step 1: It sounds like the mixer setting for your web browser is changed. To cross check if the settings are correct, try these steps.
a. Open web browser.
b. Click the volume icon on the taskbar.
c. Click Mixer.
d. From the applications list, make sure the volume icon is not mute for your web browser. If it's mute, then enable it.
e. Check if the issue persists.
See Adjust the sound level on your computer
Step 2: If you're using Internet Explorer, check if this option is enabled.
a. Click Start, type "inetcpl.cpl" and hit enter.
b. Click Advanced tab.
c. Scroll down to see Multimedia section and make sure the option "Play sounds in webpages" is selected.
d. Click ok to apply the changes and check if the issue persists.