There are several things going on here; let's take them one at a time.
Typically, the antivirus software that ships with new computers has a
limited subscription for virus updates, usually 90 days. After the 90 days
(or however long) are up, you need to either renew your virus update
subscription or purchase a new antivirus program. If you did not do this,
your computer was effectively unprotected against new viruses.
When Norton Antivirus is correctly set up and updated, it is truly unusual
for it to "miss" anything. What probably happened is that your virus update
subscription expired sometime in July.
In order for any antivirus software to be of value, it has to be configured
correctly and updated constantly. The software has to start with Windows and
stay running in the background at all times. If you're a new user you should
set all the options for maximum protection. And you must constantly update
the virus definitions. All the major antivirus programs can do this for you
automatically.
That said, even the best antivirus software will eventually fail if users do
not follow safe computing practices. You need to educate yourself on the
procedures to follow to avoid viruses (and spyware.)
Now you need to decide which antivirus program you wish to keep: NAV or
Panda. Never use more than one antivirus program at a time. Using more than
one antivirus program at a time makes your computer more likely to be
infected, not less. Whichever program you decide to keep, you must uninstall
the other.
If you decide to stay with Norton AntiVirus you will need to purchase a new
copy of the software. You're in luck there, because Norton branded software
is widely discounted and rebated, so you should expect to pay little or
nothing for the program. Be sure to uninstall your old copy of NAV before
installing the new one. Follow Symantec's uninstall instructions very
carefully. If you decide to stay with the Panda program, uninstall NAV.
You need to remove the viruses/trojans on your computer. If you decide to
purchase NAV, the program will do this for you as part of the installation.
I'm not familiar with Panda software, so I can't advise you about that.
The viruses/trojans may or may not be the cause of your problems with Word
and Excel. You won't know until after you have removed the viruses/trojans.
System Restore did not work because your computer is infected with viruses.
When one or more restore points become corrupted (which is usually caused by
a virus) you have no other choice but to erase all your restore points and
start over. You do this by turning System Restore off for all drives,
rebooting, and then turning System Restore on again. In any case, System
Restore cannot restore a computer once it has been infected with a virus.
Being a "very new user", it is especially important for you to spend the
time to learn how to use your computer. That means doing lots of reading.
Fortunately, Microsoft has lots of resources for you to start with.
Protect Your PC
www.microsoft.com/protect
How to Use Windows XP
http://www.microsoft.com/windowsxp/using/default.mspx
Good luck.
