I upgraded the operating system on both my iPad and MacBook a couple of days ago and ever since cannot open certain websites. I cannot figure out what's wrong and/or how to solve the problem!

Reinstall on both.

Reinstall Lion, Mountain Lion, or Mavericks without erasing drive

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Repair

When the recovery menu appears select Disk Utility. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported then click on the Repair Permissions button. When the process is completed, then quit DU and return to the main menu.

Reinstall Mountain Lion or Mavericks

OS X Mavericks- Reinstall OS X

OS X Mountain Lion- Reinstall OS X

OS X Lion- Reinstall Mac OS X

Note: You will need an active Internet connection. I suggest using Ethernet

if possible because it isthree times faster than wireless.

Restore your iPhone to reinstall iOS. Be sure to do this while connected to your computer and iTunes.

Tap Settings > General > Reset > Erase all content and settings.

You could try a simple reboot:

Rebooting your iDevice

Hold down the Sleep (On-Off) and Home buttons together for about 10-15 seconds or until the Apple Logo appears - ignore the red slider if it appears - then let go of the buttons. The iPad should begin to start up.

Restart your router then restart the Mac and iPad to test.

Please give an example of a website you can't open. What exactly happens when you try?