Fault finding help please

hi i have a 7 year old ecs k7s5a and i think it's coming to the end of it's life. The pc is dropping off power during start up, usually before windows password stage though sometimes after, often taking 4 or 5 times to boot up to windows, where once there, it is stable all day. my limited knowledge has got me as far as event viewer which shows nothing to help me. are there any other troubleshooting tools i can use to find the problem?

failing that, is there a way i can find compatible mobo's or mobo bundles for my rather aging pc. I'm not even sure i'd find a brand new ATX mobo with what i want, but surely there is an easier way than reading every mobo spec that is sold?

it has to be cheaper to buy a new bundle than have someone fault find the pc? but even then i might be over going OTT as the fault could be anything. It's a nightmare. ECS just put me on to their stockists and they couldn't be bothered to reply lol. i'm not looking to upgrade the spec, just want a solid working pc, what i have is fine for what i use:
ATX mobo, will need 184 pin ddr memory slot, approx 1.6athlon, agp for radeon 9600 pro, IEEE 1284 parallel port for lexmark z43 printer. not sure i can buy anything new to drop in, and buying second hand may just repeat the problem. Can anyone advise? appreciate any help thanks.