w7 switches on/off a few seconds then on/off, no boot

so 1 day W7 did not start, it starts a few seconds then stops, then continues like that.I took it to my local PC store, they said the RAM needed reseating. iT WORKED but later started the same syndrome, unable to staRT UP.
i'VE TRIED, changing RAM seats, using just 1 stick, replugging all parts inside whole PC. Just between startups sometimes, about 1 in 30 it boots as it should, rest of time not at all or with a few seconds on off?
W7 64bit O/S checked and OK
the Mobo: ASRock Z77 Extreme4-M Motherboard Intel Micro ATX Socket 1155
checked and OK
Memory: Corsair - XMS3 4G - RAM - DDR3 SO 1333 x 2 checked in Windows OK but cant use Memtest 86 the interface is different to on website, also unable to boot from Flash drive.
CPU: Processor - Intel Core i7 2600K / 3,4 GHz - LGA1155 Socket - L3 8 Mo
H/D hgst 1tb checked and OK
Wireless: TP-Link - TL-WN851N - Carte WiFi N PCI - 300Mbps - MiMo
Power Supply: Be Quiet - BQT L7-530W - ATX - 530 W appears OK
DVD R/Writer x 2
Internal multi card reader


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Re: on/off

The first thing to check: does the PC work fine if you boot from a Linux disc or stick (free to make). If it doesn't it surely is hardware. If it does work fine than, boot from your Windows 7 install disc and try the repair options it offers.

If you can't boot of a flash drive, try the DVD, both for memtest and Linux. You'll need it for the Windows 7 repair also.

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No boot

Unplug the hdd.
What happens when you try to boot?

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no boot

still nothing, off to PC shop at W'end!

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