My Computer start when it want to start

Hello,


Friends i have an acer aspire 5570z it was wokring good for 1 years upto warranty time. Than its start to behavevery strange.

First problem
Intailly i got problem with start up when i was pressing power button fan, dvd ram was starting and i was getting green light in LED. after too many try also it was not starting but another day it was staring normally. And sometime it was starting normally.

Second problem
sometime after starting up bio will display than window was unable to start and i was getting message that PXE-ROM61 media test failure, check cable, operating system not found
As sombody suggested i replace my harddisk than also i was facing same problem than i ran vista installation dvd but i was unable to complete installation. after so many try i was succeed

Third problem,

Now a days my laptop is starting normally windows also starting normally but after 30 min window is hanged i can not anything except power off.

i think may be this problem with hardware but i m not sure which hardware is causing problem
I given my laptop for repair than also they could not solve or diagonasis problem but that guy told me that may be u have problem with connector which connection harddisk to motherboard.

somebody can suggest me what i have to do

Regards,
kamlesh