I have had very similar problems. Intermittently, my PC will require 2-3 power on and offs to startup. Sometimes when I shut the pc down it shuts down but the power doesn't turn off. This can also occur, although less frequently, during auto-restart. The monitor will say that it does not detect a signal. If I leave the PC on, it is fine indefinitely.
The problem started after moving and having to pack up and then unpack and set up my PC. I'm thinking that something may have been jarred a little loose, but everything looked tight. I also tried reseating the video card anyway. I noticed that the first message I get on the screen during a successful startup is a video card check message ("SGRAM size: 8 MB), so that makes me think that it is a video card or video card slot issue. I still get the problem intermittently, but it seems to be less frequent. The video card is a Diamond Viper V330 (8 MB) Ver. 4.0. If the video card is the problem, how would a video card work intermittently, and why would powering off and on help?
OS: Win XP Pro SP2
PC Components:
Processor: AMD K6-2 300MHz (3D)
Motherboard: DFI K6XV3+ /66 revision BB+
RAM: 256 MB PC100 100-PIN SDRAM DIMMs, 3.3V
Slot 1: 128 MB, Slot 2: 128 MB, Slot 3: empty
Video Card: Diamond Viper V330 PCI 8 MB in PCI slot 1
Sound Card: Creative Sound Blaster
CD/RW drive: TEAC CD-W524E 24X/10X/40X (w/rw/r) EIDE
Internal Modem: Zoom 56k Dual Modem
NIC: Realtek RTL8029(AS) PCI Ethernet Adapter in PCI slot 2
Floppy Drives:
3 ?? 1.44 MB
Zip 100 USB External
Hard Drives:
Western Digital Caviar WD400BB EIDE 40 GB
Seagate EIDE 40 GB
BIOS: Award Modular v 6.00 PG 4/12/00