When I try and start my computer (Windows 2000) I get the following message..."check sum error...insert system restore disk in A drive". We restart the computer and get the same message. At first it would finally start correctly after about 3 times or so. The problem has grown worse. Now it takes about 30 to 45 min. to finally get the machine started. Nothing is in drive A. What could be causing this problem. Thanks for your help in advance.