Problem with monitor or graphics card

Hi! Yesterday a friend of mine gave me his old desktop,basically only the pc tower. He warned me that the pc is full of viruses and asked me to format the disk if possible. now the problem is this: when i connect the monitor and power up the pc, the monitor doesn't respon't at all! it is like i haven't connected it to the pc. I checked the cables and they are all in place. So I suspect that there must be a problem with the Graphics card. I checked the monitor to an other pc and it works fine! what can I do to find out where exactly is the problem? thanks for your time!

Yes the pc tower turns on but the monitor displays something like "no input signal,monitor going to sleep"
so i assume that there is no communication between the motherboard and the monitor.but i don't know what to do. If the monitor doesn't respond how can i communicate with the pc? :-)

try what shortstuff_mt suggested (checking on ram)... you can also test the ram on another PC and try to see if it functions. Also if you have an extra video card (functioning) try using it on that PC try to see if there is no display...