Dell Inspiron 7500 autoturn on/off & black screen

Hello ! A few days ago I bought an old laptop Dell Inspiron 7500 for my son . We originally installed Windows XP SP3 ( not boot form ) for a few days and everything went very well . But when other softwares installed on the hard disk free space there was . Therefore I decided to make a second reformation to boot from the DVD . After completing everything went very well . After that I thought to install Microsoft Office 2007 and here the problems begin . The monitor light levels was reduced as soon as the system began to recognize the Microsoft Office CD and barely seen . The laptop turned off , and the Restarting . Microsoft Office disk removed and everything was in order . The disk decided to install again , but just before the finish installing the program , the screen light level decreased . The turned off , because not seen anything . Thereafter , we monitor the laptop is not seen nothing , while when trying to ignite the burner and gives the signal turns off after 3-4 seconds, and thus continues without stopping . Unfortunately , the first CD is put in order in the BIOS ( boot ) because I had to Install Windows XP SP3 .
Please help me solve this problem because it is a very good laptop and fast, regardless of who is older and lower parameters . Thank you .