t42 display went blank

I have a t42 which is almost 4 years old and a few days back All of sudden , while i was in the middle of my work, the screen started "running down" with color lines and display went blank, only "z" status light (below LCD screen) stayed on. After rebooting the system, it came back up to WinXP with a message about "System recovered from a sever error", I clicked OK and than 30 seconds later screen went blank again. I shut down laptop for 15-20 minutes to give it a break since I had it on for the whole day. Later power it up again and even hooked an external monitor to make sure its not a problem with LCD display ribbon cable connector. Still had that intermittent problem with "running" color lines on screen and than everything going blank. Now, its constantly goes blank after the bootup and 30-40 second use.
can anyone suggest me what might have been the problem? is it the CPU overheating or might be my mobo gone bad? sometime i do get Fan error but when i reboot my machine, it works the second time. Any help is aprreciated.

 

your laptop has a video problem now. T4X series has this problem. it has something to do with the ATi7500 chip. This is a hardware problem most likely

 

Which GPU do you have? It could a poorly soldered GPU, which is a known issue on the T42.