I have a very annoying problem and my computer is acting a little strange.

Heres the story:
Brothers Computer Sat in the corner for a couple of years, Screen going on standby
Thought it may be the graphic card so i borrowed a friends but it wasn't that
Disconnected the mobo battery and put it back in. It powered up finally but came up with CMOS errors. I managed to carry on as normal so I bought a new hard drive and began installation of xp only it decided to crash while formatting at 81%.
After that it began playing silly games with me. I would power the computer on and head to the setup to change the clock settings and 9 times out of 10 it would just freeze before i even got chance to browse the other options. So i would restart the computer, only now the screen has died again and i get a long beep then a slight pause and this would repeat itself until i powered the computer down, disconnected the battery from the mobo and refitted it again. I eventually bought a new battery but still the computer would freeze and i would have to repeat the battery process to power it on. This beep and screen on standby situation is the most frustrating encounter i have had with a computer to date.

Now i had a thought, maybe their could be a conflict somewhere but i disconnected every driver. Its not that.
Checked the mouse and Keyboard. Not that
Computer freed of any dust. Not that
Ram is fitted properly.
Power supply is good, fans are keeping everything cool.
Checked, unplugged and replugged in everything.
Everything is working fine..... apart from the monitor. Is it possible that it could be a monitor/VGA lead issue? The one i have is quite old....

Something someone else mentioned to me is that the mobo bios may need an upgrade. He said after removing the battery the settings would of changed and gone back to default which COULD of caused the erratic behavior (random freezing). Anyone any idea if upgrading the BIOS might help or how i would go about it. Wouldn't hurt to try it..... (if i knew how)