Help with HP Pavillion Dv2121TX - wont boot-- Motherboard faulty?

HP Pavillion Dv2121 TX wont boot!

Specifications:
Intel core 2 duo T5600 1.83ghz
NvidiaGeforexe Go7200 up to 128mb turboCache Video memory
2gb kingston ddr2 ram
MS Windows XP Media Center Edition 2005

Notebook frequently hangs & sometimes only boots up after several days.
2 months ago, BSOD - F10 diagnostics detected hard disk failure so clean installation of MCE was done with new Hitachi hard disk but webcam, DVD-rw drive were not detected. ( motherboard problem ??)

1 month later, notebook wont boot (blue screen) following previous
shut-down after 8 hrs of use.

After a 2nd new installation of MCE, HP advised motherboard to be changed as;
1) Notebook still intermittenly can't boot up.
2) DVD drive intermittenly not detected.
3) Applications loads too slowly and hangs; (eg. Internet Explorer).
4) HP splash screen takes very long to load ( more than 2 mins).


Queries:

What is really wrong with my Pavillion Dv2121TX?

Faulty nvidia graphic chip? -Repair motherboard or change new motherboard?
Would notebook be stable after repairing and/or changing the motherboard ?

Could it possibly be a overheating problem?-(heatsink and/or cooling fan problem?) as notebook gets terrbly hot & wont boot after shutting down after long hours of use?

Pls help.
Any advice would be greatly appreciated as I know next to nothing about trouble- shooting hardware or software.

Thanks.