POST BOOTING PROBLEM

System:
Hewlett-Packard HP d530 CMT(DG061A)
Enclosure Type: Mini-Tower
Board: Hewlett-Packard 085Ch
Bus Clock: 800 megahertz
Graphics Card: NVIDIA GeForce 7600 GS
BIOS: Hewlett-Packard 786B2 v2.44 08/07/2008
Memory Modules: 2048 Megabytes Usable Installed Memory
Slot 'DIMM1' thru Slot 'DIMM4' has 512 MB
Processor: 3.00 gigahertz Intel Pentium 4
8 kilobyte primary memory cache
512 kilobyte secondary memory cache
Operating System: Windows XP Professional Service Pack 3
Hard Drive: WDC WD3200AAJB-00J3A0 [Hard drive] (320.07 GB) -- drive 0, rev 01.03E01,

POST booting problem:
The following describes the problem that my PC is experiencing:
- Turn the computer on.
- Power On Self Test starts.
- 5 sec. later on the top left-top hand side appears the graphics card description (company, model, etc.)
- 3 sec. later the HP INVENT and INTEL Pentium 4 logo appears. At the bottom of the screen it displays
<F9=Boot Menu>, <F10=Setup Menu>, <F12=Network Menu>. NOTE: if I press F9, F10, or F12, the
monitor turns black and a horizontal line blinks on top-left side of the screen.
- Computer stops/freezes for 2.5 minutes.
- Randomly, after waiting for 2 minutes, not all the time, the computer starts the Windows Booting (I hear
a click sound coming from the HDD) and I am able to work with the PC with no problems until Y turned
off.
- Randomly, after waiting for 2 minutes if the PC does not perform the Windows booting, then the monitor
turns black and a blinking line blinks on the left-top side of the screen and stays indefinitely.

Things I did to try to solve the problem:
Updated the BIOS
I tried to reset the BIOS to the default values by pressing the CMOS button for 5 sec., but never was able to get into the BIOS setup utility. I tried different ways (pressing F1, F2, F10, Del, after turning PC on) but I was not able to open/get into the BIOS utility.

Please tell me how can I force to the PC to enter the BIOS setup utility? I tried, like I say before, all the recomendations of HP and other companies, but I did not have any success. I thank you in advance for any help you can provide.