Is there a way to restore the system if I don't have the Mac OS X installation disc anymore?
No. Try calling Apple and request a replacement set of CDs for your Mac. They will charge you a nominal fee for shipping and handling.
They are part of the Mac and should be kept with it at all times.
what if i use a disc from another computer?
It will only work if they both have exactly the same hardware.
CDs shipped with Macs are hardware specific.
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