Hi all, I've got a HP Notebook worked for the past 1 1/2 years and now all of a sudden, it doesn't see it's OS in the harddisk. Ironically, after I reinstate the OS (MS Vista Home), install all other software, it gives me the blue screen after using it once or twice and all of a sudden when I boot up the machine, it suddenly can't even detect the HDD in BIOS anymore. However, after a while, it comes back to detect the HDD again after a few days, and I start reinstalling the OS and it all goes back to normal, then the cycle begins again. Few clarifications.
1. Is it the HDD that I just need to buy a new one to replace and all my problems are solved?
2. Is there anything else thing might lead to these type of symptoms? RAM, Mother board that I might have missed out. Don't want to rush out to buy a new device and found out that the root problem has not been solved.

Appreciate any advice, thanks.