Hi, i am using a compaq laptop. It is a core2duo with 2gb ram. 2ghz.
Now my problem is that sometime ago my hard disk stopped detecting. I was out of my warranty and also out of cash so didn't know wat to do.

I knew about the ubuntu live cd and so to check if it was something wrong with the laptop, i used it. it is working perfectly.

Then, by some trial and error, i also found out that if i give my laptop a real good punch or a hit when shut down and then boot into the live cd, the hard drive gets detected.

So now my process is.
1.boot.. find out that hard disk is not detected
2.boot using ubuntu live cd. still harddisk not detected
3.shut down. give laptop a real hard hit or punch.
4.Boot again using ubuntu live cd.
5.mid way through this hard disk is detected.
6.reboot... now hard disk is detected and boot into windows.
7.work like this for a day. here the hard disk works perfectly.
8.shut down.
9.try to boot next day. hard disk not detected.
10.start again from step 2

(these steps can also really help people whose data is lost. or hard disk not detecting, try it.)

p.s.i also tested the hard disk using the wd hard disk s.m.a.r.t. test and the hard disk sentinel program. It is fine. i am completely lost.

please help me. thank you.

Punch that machine enough times and it'll go south on you permanently. It's probable that there's an intermittent power connection to the drives. A repair is a big maybe. Harder on the pocket but still easier is another board.