strange hangups

I had to strange hangups today, both times while switching from tty1 to the xdm (tty7) with a machine with the following specs: AMD Thunderbird 750mhz 256 mb RAM 9Gb wd hd video card: sis630 I suspect that something that maybe pushing the frame buffer, that is what I believe is bringing the whole system to frozen state, is that I added in my lilo.conf: vga = 0x305 Could it be that? For debugging I can: a) Use memtest to test the RAM memory b) hdparm to test my drive?? c) how do I check how my sis630 video card? What other tests do you suggest for this trial & error debugging? Thanks alot, Raúl