Question about the system rebooting

hello,

i have a pc with intel 810c with 650 mhz.
and i have win98 installed on it. i have a scanner with scsi card and an internal modem.
i also have a cdrom and writer attached in the system. the problem is that it takes too long to boot thesystem. that is i hear the beep after much time. i have tried everything like changing the battery of the motherboard, reinstalled the os, and all the things like that. but the problem is still there. and once after it boots, the system gets restarted when win98 loads…….and if it gets sometimes loaded then it might work properly for 3 to 4 hours and then it get restarted on its own. i have scanned the hdd for viruses. and also i have get scanned the hdd from SYMANTEC norton online scanning services on internet.
so, please help me with the problem fasttttttttttt.

bye,
darshan