okay well a couple of days a go my mac went under a lot of lag so much it was hard to do anything on my mac so I did many things on here and many other websites to try and fix it still no luck so i decided to reformat my hdd making it fresh again so I did this and with the snow leopard install disk that was given to me with the macbook pro ( along with the app disk ) I tried to install it at the start it goes well and looks to be fine but about 10 - 20 mins into the install an alert comes up saying that it could not install properly and to restart I restarted and still it does this i have re tried about 30 times wishing for a different result and yet nothing has happened yet if any one knows why this is happening and can fix it please help me