Bootup/Freeze/Crash problem

[ASk]

System specification:

Intel Pentium III 733 (5.5x133mhz) coppermine

256mb PC133 SDRAM (at 133mhz) (2x128 sticks)

Inno3d Geforce 2 GTS 32mb DDR-RAM

IC35L040AVER07-0 (IBM Deskstar 65GXP 40GB, 7200RPM) HD

WDC AC315300D (Western Digital 15gb 5400RPM) HD - both at IDE1 channel, with the IBM being master and WD being slave

TOSHIBA XM-6702B (x48) cdrom

YAMAHA CRW8824E (x8x8x24 internal ide) cd-writer - both at IDE2 channel with Toshiba being master and Yamaha being slave

SM56 Modem

Sound Blaster 128 Vibra

Intellimouse Explorer connected via USB

PS/2 generic keyboard

The problem:

Recently (about 2 weeks) the pc started freezing during boot. Since I run Windows XP with /SOS switch, there are 3 stages: loading drivers (with the names scrolling), a blue screen with the "Windows XP SP1 5.1 running on 1 Intel Pentium 733 MHZ Processor with 256MB ram" and the checking drives stage. The system freezes at the second stage, either at the very beginning (before flashing the keyboard indicators) or at the very end (before moving to the checking disks stage). This is not constant, nor removing devices helped. Sometimes after a freeze and a hard reset (since the keyboard is locked), there's no video signal coming to the monitor, nor the POST starts (there are only the internal boot-up checks of the cd drives). Eventually it will boot normally, and after it booted it behaves perfectly stable and fine, with no freezes/crashes. (correction: system started to freeze with looping sound and locked keyboard/mouse during some of the dialings. It's not the modem though, since I tested the system without the modem in, and it still froze during bootup. Also after one of these crashes, the system didn't want to boot, stucking either before POST with no video signal or during the third boot stage, while counting down to disk check until after I powered it down completely and powered it back up)

Can anyone point me to a resourse that could help with this problem, or give a tip on how to overcome it.

Thanks in advance