So I've recently bought a pair of new ddr3 ram for my old Asus m5a97 r2.0 le mobo but it seems DIMM B2 has died, so since the mobo recommended using DIMM A2 & B2 for 2 sticks of ram would I encounter any issues or performance hits by using the ram in A1 & B1 instead?
That is a hit or miss proposition. Some boards WILL work fine with a pair of sticks in the A1 and B1 slots. Others will throw fits, or have random weirdness. Still others will simply not work right at all especially in terms of normal dual channel operation. All you can do is try. If the full amount of memory is recognized and CPU-Z shows dual channel operation on the memory and SPD tabs, at the full advertised speed, then there is no problem. If it does not, then there might be an issue with using those slots when the A2 and B2 slots are not also populated. Generally speaking, when a DIMM slot fails to work normally, it's time for a new board because that's often a sign of something else being wrong.
The first thing I'd do is pull the CPU and make sure there are no bent pins and that the CPU cooler is correctly mounted, evenly and flat. A cocked cooler with one or more mounting points that have come unpinned or are looser/tighter than the others can cock the CPU in the socket and create a variety of issues including problems with one or more memory slots.
I'd also check to see that there is no debris or bent pins in the memory slot itself, and that there are no visible signs of problems on the motherboard such as burnt marks, leaking or bulging capacitors or scratches across any of the electrical traces that might be the cause of problems with that DIMM slot.
Thanks for the reply Darkbreeze, CPU-Z show's no problem with them in A1 & B1, shows them at correct speed and in dual channel mode. I haven't really noticed a difference in performance with them in those slots but I haven't really tested it in any games or programs as yet but the computer seems to be working fine for the past 48hrs. Maybe I've hit the CPU cooler while installing them I'm not sure but atm i'm out of thermal paste so can't really re-seat the cooler atm (that thermal paste been on since 2012) heh.
If they are at the correct speed AND show in dual channel, then they are fine being used in those slots.
2012? Ouch. Time to repaste for sure. Seven years is way to long for most pastes to still be doing their job well. Anyhow, should be fine with them in those slots though. I'd keep an eye on things to make sure no further problems develop beyond just that slot not working though.