HP dv4-1540us laptop - help me pinpoint the problem?

I am facing all kinds of strange problems with this laptop for last few days.
The laptop is under warranty and had already made one trip to HP Repair center about two months back - at that time they repaired/replace motherboard and re-imaged hdd.

I tried chatting with HP support people but it was not much helpful this time. Since I need to use this computer on a day-to-day basis, if possible I would not like to send it again to repair center.

Now most of the errors occur while booting but the strange part is that gives different errors at different times. Here are examples of errors I have faced:
1. "No hard disk found" -- while booting.
2. Blue screen error -- after windows initial welcome screen is shown (the one before the login screen)
3. Black empty screen with a mouse arrow showing - after HP welcome screen
4. Sometime it will start completely and then I will get a blue/black screen after 5 minutes of using the laptop.

Things I have tried:
1. Hard disk self test - tried like 5 times over last 1 month - 3 times it got stuck in between and 2 times it passed.
2. Ran Windows system file checked - no errors found.
3. Ran memory test and all other tests available at booting level
4. Tried system restore - of course did not help.
5. Put a working hard disk from another dv4 laptop into this laptop - it worked perfectly.
6. Put this hard disk into the working dv4 laptop - gave errors.

Note that the laptop still works....it is just that almost every other day. I get an error at boot time. I try like 4-5 times and then it eventually boots and lets me work.
Also, hp will only replace hard drive only if it fails the hdd self test.

So, please help me out and tell me what I can try to pinpoint the exact problem and possibly solve it without sending the whole computer to hp repair center.

Thanks

 

I'm guessing you you're running windows 7. Was there a specific program you installed after which the program started acting up? Is this plugged in or on the battery. If it's the former, I'd try uninstalling the software. If you were on a desktop I'd say you have a power supply problem. Do you have the problem when you're plugged in or booting from the battery?

 

Definitely sounds like the hard drive is going to me.