If it is affecting multiple browsers (that is to say, the entire computer) but you can ping external IP Addresses fine, and there isn't any software blocking traffic on that computer evidently, then I'm back to DNS issues.
Are you using your ISP's DNS servers?
You might try using Google's, just to see if it makes a difference. (188.8.131.52 and 184.108.40.206)
You can either reconfigure your router to use them or just change them on your computer. (exact process will vary depending on your OS but basically you'll change you IP configuration from dynamic to static, use the same IP address that your router had assigned, and use the same default gateway, just change the primary and secondary DNS servers to the ones above)
RAID protection is only for failed drives. That's it. It's no replacement for a proper backup.