Help with PC associating to a far away access point

Question

We have an issue in a training room where 4 Dell all in one PC's sometimes have wireless issues.  We relocated the AP to directly above the 4 PC's instead of the hallway outside of the training room because off that hallway there is also a lunch room with two microwaves, so we thought that was interfering.
Anyway sometimes one or two of the PC's in this training room fall off the wireless or they must be associating with the AP on the 3rd floor causing the latency to go in upwards of 1900ms in ping times to the machine.  Rebooting the PC will usually bring it back to the AP directly above it, resulting in ping times of 1-3 ms.
I drew up a very summarized diagram and what I am thinking is happening is that the wireless signal is bouncing around an emergency stairwell located in the back of the building that has direct access to the 3rd floor, and also that AP on the 3rd floor is at that end of the building near that stairwell.  Employees don't use this stairwell, there's two others and also an elevator in the building.
We have a 5508 WLC running on 7.4.121.0 and 6 AP's in this building.  Just curious if there is anything I should be checking on the WLC, or do you think this is a PC network card problem where I should be checking drivers, etc...
We could throw a small switch in there and hard wire them, but we got all in ones with wireless because the desks are on castors and being that it is a training room, sometimes they like to move things around in there.

Answer 1

Ok, I checked for both 802.11a/n and 802.11b/g/n,
TPCv1 checked.
Power level assignment method - automatic every 600 secs
Maximum power level assignment 30
Minimum power level assignment 11
Power threshold -70
DCA for 802.11a/n -
Channel assignment method - Automatic - Interval 10 minutes - AnchorTime 0
Avoid Foreign AP Interference - Enabled
Avoid non-802.11a noise - Enabled
DCA Channel Sensitivity - Medium
Channel Width 40 MHz
DCA Channels: 36, 40, 44, 48, 52, 56, 60, 64, 100, 104, 108, 112, 116, 132, 136, 140, 149, 153, 157, 161
Extended UNII-2 Channels enabled
Event Driven RRM Enabled, Sensitivity Threshold - Low
DCA under 802.11b/g/n
Channel assignment method - Automatic - Interval 10 minutes - AnchorTime 0
Avoid Foreign AP Interference - Enabled
Avoid non-802.11b noise - Enabled
DCA Channel Sensitivity - Medium
DCA Channels 1,6,11
Event Driven RRM - Enabled
Sensitivity - Low
Now lets look at data rates.
802.11a global parameters
6,9,12,18 mbps all disabled
24 mbps Manditory
36,48,54 mbps Supported
Beacon Period - 100
Fragmentation Threshold 2346
DTPC Support - Enabled
Maximum Allowed Clients - 200
802.11a band status Low, Mid, High all enabled
CCX Location Measurement - enabled - 60 seconds
802.11b/g global parameters
1,2,5.5,6,9 mbps - disabled
11 mbps - Manditory
12 through 54 Mbps - Supported
802.11b/g network status and 802.11g support - enabled
Beacon - 100 ms
Short Preamble - Enabled
Fragmentation Threshold - 2346
DTPC Support - Enabled
Maximum Allowed Clients - 200
CCX Location Measurement - Enabled - 60 seconds
Now for the SSID these systems are connecting to,
Client load balancing is unchecked
Client band selected is checked
Coverage hole detection is enabled
MFP Client Protection is optional
DTIM Period is 1 for both a/n and b/g/n
In the trap logs, some of the things I see frequently are:
Interference Profile Failed for Base Radio MAC: 58:35:d9:39:5b:40 and slotNo: 0
Coverage hole pre alarm for client[1] c0:63:94:52:01:cc on 802.11b/g interface of AP 58:35:d9:39:5b:80 (AP3). Hist: 46 14 2 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Interference Profile Updated to Pass for Base Radio MAC: 50:1c:bf:80:5f:d0 and slotNo: 0
And also a bunch of Rouge AP detected or removed from Base Radio MAC.
Hope some of this information helps.  It seems that the training room computers have more difficulty when there are people next door with 4 laptops.  Still that would only be 8 clients on one AP.  That AP has a 1 gig connection to a 3750 switch port.