Ubuntu – Not all cores registered, Ubuntu 14.04 i7-2630QM

I'm not sure when this happened, but for some reason my processor is only using two out of 4 physical/8 logical cores.

I've tried to remove acpi=off from /etc/default/grub with no luck. I've changed graphics driver from Nvidia proprietary to X.org, no dice. There's no settings for cores in the BIOS. I've asserted that CONFIG_SMP=y is in /boot/config-3.13.4-49-generic.

I have permanently pulled the laptop battery out, since it is totally bust (20 seconds capacity). Might that be the reason? Also, I recently downgraded from 14.10 to 14.04 by way of a complete reinstall. My computer is an Asus X53sv.

What's left to do? I want to avoid a complete reinstall, if possible.

alrekr@alrekr:~$ cat /proc/cpuinfo
processor   : 0
vendor_id   : GenuineIntel
cpu family  : 6
model       : 42
model name  : Intel(R) Core(TM) i7-2630QM CPU @ 2.00GHz
stepping    : 7
microcode   : 0x1b
cpu MHz     : 1995.622
cache size  : 6144 KB
physical id : 0
siblings    : 2
core id     : 0
cpu cores   : 2
apicid      : 0
initial apicid  : 0
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer xsave avx lahf_lm ida arat epb xsaveopt pln pts dtherm tpr_shadow vnmi flexpriority ept vpid
bogomips    : 3991.24
clflush size    : 64
cache_alignment : 64
address sizes   : 36 bits physical, 48 bits virtual
power management:

processor   : 1
vendor_id   : GenuineIntel
cpu family  : 6
model       : 42
model name  : Intel(R) Core(TM) i7-2630QM CPU @ 2.00GHz
stepping    : 7
microcode   : 0x1b
cpu MHz     : 1995.622
cache size  : 6144 KB
physical id : 0
siblings    : 2
core id     : 1
cpu cores   : 2
apicid      : 2
initial apicid  : 2
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer xsave avx lahf_lm ida arat epb xsaveopt pln pts dtherm tpr_shadow vnmi flexpriority ept vpid
bogomips    : 3991.24
clflush size    : 64
cache_alignment : 64
address sizes   : 36 bits physical, 48 bits virtual
power management:

Edit Inspecting /var/log/kern.log as suggested in a comment revealed (all lines repeated throughout the file) the following. I suppose this hints to a malfunctioning CPU?

Apr  7 08:08:03 alrekr kernel: [    0.000000] MPTABLE: Product ID: _ASUS_
Apr  7 08:08:03 alrekr kernel: [    0.000000] MPTABLE: APIC at: 0xFEE00000
Apr  7 08:08:03 alrekr kernel: [    0.000000] Processor #0 (Bootup-CPU)
Apr  7 08:08:03 alrekr kernel: [    0.000000] Processor #2
Apr  7 08:08:03 alrekr kernel: [    0.000000] IOAPIC[0]: apic_id 2, version 32, address 0xfec00000, GSI 0-23
Apr  7 08:08:03 alrekr kernel: [    0.000000] Processors: 2
Apr  7 08:08:03 alrekr kernel: [    0.000000] smpboot: Allowing 2 CPUs, 0 hotplug CPUs

Apr  7 08:08:03 alrekr kernel: [    0.063101] smpboot: CPU0: Intel(R) Core(TM) i7-2630QM CPU @ 2.00GHz (fam: 06, model: 2a, stepping: 07)
Apr  7 08:08:03 alrekr kernel: [    0.063115] TSC deadline timer enabled
Apr  7 08:08:03 alrekr kernel: [    0.063123] Performance Events: PEBS fmt1+, 16-deep LBR, SandyBridge events, full-width counters, Intel PMU driver.
Apr  7 08:08:03 alrekr kernel: [    0.063130] perf_event_intel: PEBS disabled due to CPU errata, please upgrade microcode

Apr  7 08:08:03 alrekr kernel: [    0.064825] x86: Booting SMP configuration:
Apr  7 08:08:03 alrekr kernel: [    0.064827] .... node  #0, CPUs:      #1
Apr  7 08:08:03 alrekr kernel: [    0.078239] x86: Booted up 1 node, 2 CPUs
Apr  7 08:08:03 alrekr kernel: [    0.078243] smpboot: Total of 2 processors activated (7982.56 BogoMIPS)

Apr  7 08:08:03 alrekr kernel: [    0.000000] No NUMA configuration found
Apr  7 08:08:03 alrekr kernel: [    0.000000] Faking a node at [mem 0x0000000000000000-0x000000024fdfffff]