Avast7 vs Windows XP

[delonyung]

thanks for reading my bad english....

I have a pc infedted by virus ramnit, heur, or more (i really dont know) which cause by putting usb removeable disk at 15 dec 2011. lets say those pc is PC A
PC A is a desktop using windows XP... i use PC A for my store using POS(point of sales) local program. note i already use that program for 4 years an i got no problem.
PC A still running with no problem even it was infected by viruses.

then at 3 febuary 2012 i need to get my backup database from PC A. after i get the database to my removeable disk, i use a clean desktop PC with windows 7 and avast 6 (last update 15 or 16 january 2012)
to clean the virus. it was successful.

the problem come today 1 march 2012. after i get my backup database from PC A which still infected by viruses (i am certainly sure that those viruses still the same because PC A never connected to internet
and never contact with anything) , i use my notebook to clean the viruses. my note book use windows XP pro, SP2, and avast 7 updated to 1 march 2012. the viruses cant be removed and my notebook crash and
cant even log in (when i click login to administrator or user.....they always said logging off....saving system....)

for detail when i try to clean the removeable disk which contain the viruses avast detect the viruses....pop up..etc.....after that avast ask to restart and scan the viruses....thats the real problem begin.
after i restart and scan the system.....i delete the viruses....then i cant login to windows :"(

this what i ask..... why the first time (win 7+ avast 6) can removed the virus succesfully , but when i use my note book (win XP +avast 7) the viruses cant be remove+ my note book crash...
thanks again...

[Khanat]

I suspect your problem is caused by Windows System Restore. All versions of Windows starting with Windows ME which dates from 1998 include System Restore which makes a backup of every executable on your machine. Unfortunately, that also includes viruses.

What you need to do first of all is to delete all your previous System Restore points to remove the viruses from the protected folder which antivirus cannot access. In Windows XP, you can find System Restore by going to Start | Programs | Accessories | System Tools | System Restore. Disabling it removes all previous Restore points which contain backup copies of the viruses.

Then do a full system scan to remove all infections and then reboot. Once the system has been cleaned, you can re-enable System Restore again.

As an extra precaution, download he free version of Malwarebytes from http://www.malwarebytes.org/products/malwarebytes_free and run a full system scan just in case Avast misses something.

[delonyung]

first of all i thank u for replying...
but i think u miss the real question...

review:
1. PC A which is my pc infected by virus ranmit, heur,.....or more
2. PC B is the desktop i used to clean the virus....and it was sucessfully (i used win 7 and avast 6 updated to 15 january 2012)
3. PC C is my notebook (i used win XP and avast 7 updated to 1 march 2012)

when i get my backup from PC A and use PC B for cleaning the virus, it was sucessfully
when i get my backup from PC A and use PC C for cleaning.....the virus cant be remove instead infected my PC C

i can not clean PC A because the anti virus deleted all exe if it was infected....it will shut down the POS program and i cant get my backup

my question is: 1. why avast 6 (updated to 15 jan 12) is better than avast 7 (up to date until today).........."OR"  my win 7 and my win XP is the problem
                       2.(the important one) if i use my win 7 + avast 7(because i already updated) can it remove the virus from my removeable disk completely?

because i really need that data... but i cant afford if all my computer is infected by virus.....i just need to clean my removeable disk....i just want to make sure if i used win 7+ avast 7, they can remove
the virus from my removeable disk completely.... the PC can be reinstalled, but the data from PC A is very important to me

thanks.....and sorry again for my bad english