What kind of memory modules does it have? Does it boot into CMOS? Giving the RAM "a bit of a clean" means exactly what? - Have you tried another memory module?
Try here and see if you can work out what the error beeps mean.
OnePlus 5T review: Hands-on
Illustrator Andrés Lozano on his improv line work, brazen use of colours & hand sketching
iPhone X review
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