Hi there, as the Virus A is the oldest model (released around 1997), it sounds like the battery may simply need replacing as it holds the data when your Virus is powered off.
It's a standard CR2032 lithium battery, they're round and flat:
They're readily available pretty much everywhere. You only need one.
You will need to open up your Virus to replace it. Make sure the Virus is disconnected from the mains electrics when doing so.
The Virus A may look similar to the Virus Indigo without its keyboard, so you may wish to take a look at my dis-assembling a Virus Indigo thread to have a quick squizz to see what it's like under the hood:
http://www.infekted.org/virus/showthread.php?t=31443
I've circled the round CR2032 battery:
No soldering required, looks like you can simply slide out the CR2032 battery and insert a new one.
Close up:
