HELP! This is driving me crazy

Hi,
Basically my browsing experience has become very erratic. Some websites I can access, but mainly I can't, due to a "NOT FOUND The URL was not found on this server". I'm very lucky to be able to access this forum to try and find out why I'm having problems, as most I can't.

It wouldn't be so bad if it was just Safari (my browser of choice). It happens with Chrome & Firefox as well.
My first thought was to contact my ISP, and they did all the checks they could and returned no problems. I even tried a different router, which suggests it's a Mac-based problem?

The basics: iMac; OS 10.6.8; wired router connection.

Apart from the "url not found..." sometimes the web page will try and load and then hang. Youtube for instance will open, but when I search for a video, it goes straight back to "Not Found, etc..."

I've not downloaded any software and installed it on my Mac. I've even run ONYX to see if it could find a virus, but nothing.........!

I know that the websites that return an error are working - ie the BBC website for instance.

Any ideas?

Thanks

How are you connected to the net? WiFi? Wired? What are the exact mac specs?

Asking because with 3 different browsers doing the same thing, that is strange. Also do you check email or chat or use any other internet application and if so, do they work normally?

I'm connected by wired ethernet. My exact Mac specs are iMac 9.1, Intel Core Duo, 2.93 GHz, 8Gb Memory.
I've only started encountering this problem in the past couple of days. I've tried using different DNS servers, run hardware tests, flushed all caches, etc. Reset Safari. I think I've pretty much tried all avenues?
I only use email, and they seem to be fine...

Do you have an anti-virus installed?

The only thing I have installed as an anti-virus measure is ClamXav Sentry

I wonder if this is a failing DNS issue. Try switching to OpenDNS with these instructions to see if things improve.

Thanks for that but I'd already tried using Open DNS plus Google's version...

How old is the modem/router? For me three years seems to be about the maximum useful life of these units then get the dropping out, not connecting and URL not found errors.

I have had the same symptoms with a bad modem, bad router, and bad cabling. I had a noisy ethernet drop one time and spent quite a long period of time troubleshooting it. I didn't have wireless at the time and only one computer in the house. Finally moved my computer, bypassed all network wiring and connected with a new cable right to the cable modem. Problem went away. Started backtracking and found the ethernet plug connection at the router was defective.

Bill

Well, the router is only a couple of months old. And I hear what you are saying about the ethernet plug connection being faulty - that's interesting.
I'm going to try and see if I can connect wirelessly.

Update:
I connected my computer wirelessly and same problems. I borrowed a laptop, connected using my wireless network, signal strength showed as excellent and no problems accessing the sites I couldn't!
This got me thinking back to a few days ago, and I remembered my Mac started making these odd whirring noises - a bit like it was trying to eject a disc but couldn't. This whirring sound lasted a few minutes and then stopped. I'm thinking that this MIGHT be the root cause. If it is, why would it make my internet browsing so erratic?
Thoughts, please....

The first thing to do is check your hard drive to see if there may be any problems. Use Disk Utility either from your boot install DVD or if you're running Lion or Mountain Lion, run it from the recovery partition. If the hard drive checks out OK, it might then be a good idea to run the Apple Hardware Test.

You might also want to create another admin user on your machine, log into that user, and try again to access those web sites. You have to try and determine if this is a hardware or software problem.

Thanks chscag, I'll try that....

Update:
I used disk utility, verified disk and disk permissions. I'm no techie but it did say that:
"Warning SUID file/library/core has been modified and will not be repaired"
Whatever that means!
Anyhow everything else seemed to be OK. "SMART status was verified"
I wasn't able to run the hardware test as I only seem to have one disc for when I upgraded to Snow Leopard. I bought this mac second-hand and no discs came with it.
Using another admin account showed the same problems...

Do not worry about SUID warnings - just ignore them. For what it is worth Apple Online still sell the Snow Leopard OS X.6 discs for $19.99 great troubleshooting tool to check the state of the hard drive etc.


http://support.apple.com/kb/TS1448

Good that you were able to determine the hard drive and permissions are fine. The fact that using another admin account shows the same symptom means that whatever it is, affects the main system.

I don't normally recommend a reinstall of OS X, but in your situation I think I would try it. Since Snow Leopard will do an automatic "archive and install" you won't lose data or documents. However, if you decide to go that route, make a backup first just in case.

Just done a reinstall of the OS - ****, everything STILL not working properly....