Okay so my friend owns an internet cafe and I'm likely their techy guy. So suddenly one of the desktop computer got a blue screen. Then I've tried reformatting the drive with windows and now whenever the Windows xp logo + loading dissappears, it turns to black screen and with a cursor on the center.
The reformatted hard drives works with the other computers. So there must be a hardware problem in here.
From your post I understand that after Blue Screen of Death (BSOD), you formatted the Hard Drive and reinstalled Windows XP. After this when the computer tries to load Windows the screen goes blank after Windows Splash screen appears. The symptom indicates that a faulty video card driver might be causing the problem. Try the below mentioned steps and see if this fixes the issue:
1. Power on/Restart the computer.
2. Once the computer goes past the initial setup screen start tapping the F8 key on the keyboard.
3. It will show you Advanced Boot Options.
4. Select Safe Mode and hit Enter.
5. After loading some initial drivers the computer will show you the Desktop with a low resolution. While you are still in Safe Mode uninstall/install the Video card driver.
6. If you need any help with the video card driver installation, do reply with the Device instance ID of the video card driver.
7. To get the Device instance ID of the video card, right click the Computer/My Computer icon on the Desktop, select Manage, select Device Manager under Computer Management from the left pane, then expand Display Adapter from right pane. Right click the Device listed under Display Adapters, click properties, go to the Details tab, and then select Device Instance Id from the dropdown list. Make a note of this Device Instance ID.
As you have mentioned your removed the video card and tried onboard video still the same problem occurred, so it is not the video card.
When the computer tries to boot to safe mode, it will try to load the generic drivers for some basic components in the machine. If any conflict happens during this process it might stop the boot process or reboot the computer.
Try removing any addtional components in the machine, such as video card, sound card, modem card, or any other expansion card(s), also remove the optical driver or any other external peripheral which is not required during the boot process. Then try to boot and check if there is any success.