Inspiron 1520 won't boot! Help!

It's driving me nuts! My 1520 just won't start, it doesn't even show me the Dell logo at the beginning.
The weirdest thing is that it randomly starts (one out of 20 attempts), and runs smoothly. When it doesn't start, it spins up the HD and the DVD, but after 5 seconds both go off and the computer remains on (the little power LED remains on).
I've already contacted Dell, and they told me that I should send it to them, that the warranty covers it (fortunately!). The thing is that I'm worried it might be because I've installed (many times) some new OS: Vista Business, Debian, Ubuntu... and I don't know if they could be responsible for the damage.

Does anybody have the same problem? Can someone help me?
Thanks!

 

Did it just start happening or did things slowly start going wrong?

 

i had the iddentical problem with an hp pavilion so i dont think it is the os cause i never installed another one
btw wen it starts up does it make a couple of noises

 

yeah i think it's not a software issue. it could be the wiring inside. have you tried to check if the AC adapter is causing the problem (loose connection/cable)?

 

well, it just started happening. I turned it off, went to sleep, and when I woke up it didn't boot all of a sudden. I managed to turn it on, so right now I'm making a backup of my HD on my desktop pc.
It doesn't make any noise, apart from the spin-up of both the HD and the DVD.
About the AC adapter, I don't know exactly how to test if it is well or not, but it has still the green LED on, and the computer shows the exact same problem when I turn it on with the battery and no AC connection.

 

have u tried using an other hd

 

No, but I'll try now. Thanks! I'll let you know when I'm done (probably today in the afternoon).

 

Actually it wont be a HDD problem because you are not even able to see the DELL logo screen which it takes from the BIOS only.... That logo screen should show up if you just have your CPU, Motherboard, RAM and Display working properly..... I believe it might be some loose connection somewhere or some soldering might be a lil loose somewhere..... It might also be a motherboard problem..... Better ask DELL to replace your motherboard or your laptop itself...

 

I've recently contacted Dell and they told me that it might (should) be the graphics card got damaged by a power surge, that it happens more often than you'd think, and that my warranty will cover it. If it isn't the graphics card (nVidia GeForce 8600M GT), then it's the mainboard, which is also covered by the warranty.
Thanks everybody for your help!.