I am having some trouble with my computer. Can anybody ease my pain?

Yesterday, i suddenly found my LAN card uninstalled automatically, so i opened the casing to adjust the card on its slot. While doing this my monitor's data cable to AGP card was so hardly attached with the port that i had to make an effort to unplug it (at this point, i dont know whether it moved the card from its slot or not.) when i restarted the PC, it seemed ok i.e. it found the LAN card properly installed and nicely ran for a while but all of a sudden it hanged and automatically initiated to restart but failed to do it. Since then every time i switch on my PC, it does nothing but gives a couple of beeps (the monitor remains blank). I unplugged the AGP card and plugged it again properly but my PC seems never to regain from this problem. i fear whether my hard disk has been crashed or is there any other problem? I cant figure it out. Can anybody plz help me?