Cann't open pages in internet and system-restore disabled!

One of my PCs still using XP and has the above mentioned issues since about 7 days ago! I could ping (wired connection) my ISP (Plusnet's FTTC) Gateway, its associated DNS Servers 1 & 2 through my Plusnet router, but cannot open any pages/web sites either using Firefox or Internet Explorer. It always gave me "Server not found" error prompt in my browser if I did trying to open any pages through my internet connection. I knew my internet connection is perfectly O.K because my other 3 PCs and Smart phones can access the internet O.K through the same router via wireless or wired connections.
Beside that, whenever I tried to use Windows Restore to restore my problematic PC back to previous known system states, but my windows always said "The system makes no changes" even after it had gone through all apparent restore processes and rebooted.
So is it a SIGN of security alert or virus infection in my above PC because I would have thought the Windows Restore function should have been functional rather than being disabled as well!!!! I have scanned my PC with Malwarebytes and Avast in separate occasions via their 7 days OLD definition files (because I cannot access to my internet to update their files) and found nothing . So is there any GOOD standalone virus scanner/s, being able to install in either DVD or USB memory, that I could use to decide if my PC is INFECTED and causing my above mentioned internet issues???

Many thanks

you could download a standalone virus scanner which was up-to-date, and burn it to optical disk or USB.

Have you tried to ping something further afield to see how much works (my favourite is google.be as it always replies, and is short to type)?

After that, I'd try booting a linux standalone CD/DVD or usb, which should set itself up to use your hardware and be able to browse the internet (if your hardware works).

It's just possible that you have a hardware NIC problem

Thank you for your suggestion!! Previously I was incorrect in saying that I could "ping" my ISP's DNS Servers. In fact it was a "Test" ran inside my router which indicated that I could connect to their DNS Servers O.K and consequently I was made to believe that my broadband and internet connections could go as far to my ISP's Server and PPP etc was therefore O.K.
However when I executed the "Ping" command in CMD inside Windows XP, I then discovered that I couldn't reach any body or web sites. I downloaded Linux Mint 17 Mate ISO and created a bootable DVD for testing my hardware purposed. After the Linux Mint bootup in DVD, I can use my internet with Firefox perfectly O.K, i.e. I could surf the net perfectly O.K. as I previously did in XP before I started to have these problems. Therefore I could conclude that my NIC hardware in this problematic PC is working, and some how my existing Windows XP OS/files got corrupted. Since I have NO recent backups nor Windows Restore was working, I have already ordered a Windows 7 Pro 32-bits (for maximum compatibility with some of my previous XP programs) FULL Installation DVD and its product code so that I can have a "clean-install" to replace my outdated XP for that PC. In doing so any SW hickups or even virus infections should be cleaned up after I reformating the harddrive prior to installing W7!!!
Thanks for your valuable suggestion!!

This is just a followup of what I wanted to do really! I clean-installed the Windows 7 Pro to wipe out this problematic XP PC. The W 7 installation went through painlessly compared to previously messing about the XP's non-opening sites issues. Although I had to reboot many times after installation of Windows 7 for updating the newly installed OS, so far I has had no complains apart from I have to re-install/missing-out some programs I wanted to keep in W 7 environments. So far so good because whatever causing my previous XP's OS problems, I would simply leave it behind after this W7 upgrades!!

P.S: I seemed to have noticed that Windows 7 Pro doesn't come with an E-Mail program??? Is it true or I'm actually missing something????

P.S: I seemed to have noticed that Windows 7 Pro doesn't come with an E-Mail program??? Is it true or I'm actually missing something????

Correct. Microsoft chose to disable Windows Mail just prior to the release of Windows 7 however left all of the necessary components in place. All that is required is to replace msoe.dll with a working version from Vista and to add a number of registry entries.

PM me if you want further details.

MM

Thank you for the reply! I have since installed "Thunderbird" e-mail client and set up all my existing e-mail accounts using that with great success. I prefer to stay it that way rather than purely relying on MS. Above all I can always switch to other 3rd party e-mail clients if I wanted to.

Thanks for the reply!!

mailwasher is a good email client with multiples of antispam lists aswell but for the free side you can only have one account.

I've installed Thunderbird in my newly installed Windows 7 and start feeling happy with it! Thanks for the suggestion.