760, power button steady amber and blinking 3 and 4 lights

Hi

You should take a picture.

You're right with troubleshooting the RAM.  Orange light on the MB is normal and means it has power.  With the problems you're still having, I wonder if the DIMM slot(s) went bad.  Make sure they're clean if you didn't already.

Did you try reinserting RAM one at a time and power up after each stick?  That could help you troubleshoot if it's RAM or DIMM slots.  What brand of RAM does it have?  Kingston Value RAM (KVR) rarely works in Dell's.  The volts can be off in off-brands.  Crucial comes recommended because it's guaranteed to work in Dell's.  At the very least, the chips should be same brand and MHz, besides size.

Dell Diagnostic Lights

About cleaning the ram slot, could you please tell me how this could be done? I dont really know any safe method to clean it. Thank you in advance

I already reinstall the ram one at a time and power up but it wont start. I also install the rams in all the 4 DIMM slots one at a time...still doesnt work. The pic with the 4 rams shows the rams that was installed on my computer initially and they all worked perfectly simultaneously. The pic with the 3 rams shows the ram that i got from my neighbour. I know that both mine and my neighbour's are DDR2 rams but i dont know their respective Mhz.

Small brush attachment on the hose of a hand vac.  You know how a vac can grab things without a brush attachment?  That's what we're avoiding.  It's also the way I keep my computer(s) clean.

Some people might use compressed air to clean computers, but I don't believe in spreading the dirt all over.

Dell diagnostics doesn't say anything about if 3 & 4 are blinking.  I still ended up thinking they were on steady.  Steady orange power light means the system can't process data.  If that was by itself, it would mean a possibly bad MB.

RAM speed should be on the stickers that the RAM comes with.

Unless you know you did it more recently, try replacing the CMOS battery.  The 760 is 10 yrs. old and the battery is good for about 5.  Naturally, lithium is recommended over alkaline.  Low batteries can cause all sorts of bizarre problems.