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Check this one out, my son upgraded the CPU,motherboard and power supply in his gaming PC .I was left with an amd a6 apu( that's a CPU and graphics chip in the one unit,who knew) ,a gigabyte f2a55m-hd2 motherboard ,and a 500watt power supply spare .I stuffed them all into a gutted xp era Compaq presario case ( circa 2007)I found in the attic .Added an old 160 gig hard drive and a 4gig ddr3 ram stick.The thing boots up in seconds and is fantastic for watching videos.see pictures below.
Yes, well done in stitching all the parts together and making something useful out of them. It sounds a bit like a 'Frankenstein' operation. Maybe you could use the reborn computer as a test bed for various Linux operating systems.
Just checked and the parts like these can be had for a fraction of what you would pay for an already built PC in say PC world.It isn't so hard to put it together .For instance that apu comes with thermal paste already applied,also practically all PC cases are atx now meaning the motherboard will fit no problem.