Sony Vaio bootup problems

I have a weird dilemna.

My laptop VGN-FS640 suddenly won’t boot up. It does so intermittently when I hold Ctl-Alt-Esc and then only with the Windows XP Pro disc in it. And yet only intermittently. I reinstalled WINXP PRO and it restarted, only to have the same problem recur.

I’m getting desparate; can’t afford a new computer and this does function well enough for my needs. Could somebody please help me; point me in the right direction?

My best thanks in advance,

Michael