My computer turns on and gets to the HP invent logo , turns black , turns off and on repeatedly .

[Walwis]

Product :HP Pavilion dv2000

[WAWood]

@Walwis 

The Hp logo is encoded into the BIOS chip on the motherboard, so it will display even if there is no drive in the laptop.

This issue is often due to a failing drive.

So, let's check that first, because if it is failing, it would need to be replaced and there is no point then in doing anything else until we confirm that.

If your PC is new enough to support UEFI, you can use these steps to test the HDD (Hard Disk Drive): http://support.hp.com/us-en/document/c00439024

If not, to check the HDD you have to follow these steps:
1) Press Esc key repeatedly, several times a second, while rebooting the laptop. Do NOT hold the key down, just press it over and over.
2) Eventually, you will see an HP Startup Menu
3) Press the Function key for testing the hard drive (usually F2) and let it run.

If the drive checks out OK, then report that and I can provide you options for reinstalling Windows on your PC.

Please note that if your model has an SSD instead of an HDD, these diagnostics might not work properly.