my desktop doe's not start up

my young son was on the internet playing a game when it shut down, other son step in and saw the an config update came on and then shut down it self. Then my daughter went on it, start up on bios first then there a few words and microsoft corporation can on with light flashing side to side but no welcome screen and no password can you help

If the pc won't boot, does it show an error message? Have you tried booting into safe mode (start tapping f8 when booting), this will show a menu. safe mode will be at the top, this should start Xp with minimum amount of drivers loaded, you shouldget to a desktop & be able to run a system restore at this point

from what you say I think you have a virus
Also based on what I've seen with recent infections I don't think its an easy one to fix. Time to call in help
I've had three in the last week where boot fails at the login screen, and even running a manual restore of the registry fails to get it going. I'd guess you need to backup data and reload the machine - and you will need help for that