I did an EtreCheck scan, here's what it says, maybe it can help to find the problem.
EtreCheck version: 2.1.6 (109)
Report generated January 21, 2015 at 12:15:35 PM GMT-5
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Etresoft: EtreCheck
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Hardware Information:

iMac (27-inch, Late 2009) (Technical Specifications)
iMac - model: iMac11,1
1 2.66 GHz Intel Core i5 CPU: 4-core
8 GB RAM Upgradeable
BANK 0/DIMM0
2 GB DDR3 1067 MHz ok
BANK 1/DIMM0
2 GB DDR3 1067 MHz ok
BANK 0/DIMM1
2 GB DDR3 1067 MHz ok
BANK 1/DIMM1
2 GB DDR3 1067 MHz ok
Bluetooth: Old - Handoff/Airdrop2 not supported
Wireless: en1: 802.11 a/b/g/n
Video Information:

ATI Radeon HD 4850 - VRAM: 512 MB
iMac 2560 x 1440
System Software:

OS X 10.10.1 (14B25) - Time since boot: 5:59:9
Disk Information:

WDC WD1001FALS-40U9B0 disk0 : (1 TB)
EFI (disk0s1) <not mounted> : 210 MB
Macintosh HD (disk0s2) /Volumes/Macintosh HD : 921.70 GB (264.24 GB free)
Recovery HD (disk0s3) <not mounted> [Recovery]: 650 MB
BOOTCAMP (disk0s4) <not mounted> : 77.52 GB
OPTIARC DVD RW AD-5680H
USB Information:

Seagate BUP Slim BK 2 TB
EFI (disk1s1) <not mounted> : 210 MB
MAC (disk1s2) / : 1.50 TB (1.49 TB free)
Recovery HD (disk1s3) <not mounted> [Recovery]: 650 MB
PC (disk1s4) <not mounted> : 500.05 GB
Apple Inc. Built-in iSight
Apple Computer, Inc. IR Receiver
Microsft Microsoft Wireless Optical Desktop® 2.20
Apple Inc. BRCM2046 Hub
Apple Inc. Bluetooth USB Host Controller
Apple Internal Memory Card Reader
Firewire Information:

WD My Passport 071D 800mbit - 800mbit max
disk2s1 (disk2s1) <not mounted> : 32 KB
disk2s2 (disk2s2) <not mounted> : 29 KB
disk2s3 (disk2s3) <not mounted> : 29 KB
disk2s4 (disk2s4) <not mounted> : 29 KB
disk2s5 (disk2s5) <not mounted> : 29 KB
disk2s6 (disk2s6) <not mounted> : 262 KB
disk2s7 (disk2s7) <not mounted> : 262 KB
disk2s8 (disk2s8) <not mounted> : 262 KB
My Passport Studio (disk2s10) /Volumes/My Passport Studio : 1.00 TB (69.18 GB free)
Gatekeeper:

Mac App Store and identified developers
Problem System Launch Daemons:

[failed] com.apple.ucupdate.plist [Details]
[failed] com.apple.watchdogd.plist [Details]
User Login Items:

None
Internet Plug-ins:

Default Browser: Version: 600 - SDK 10.10
QuickTime Plugin: Version: 7.7.3
3rd Party Preference Panes:

None
Time Machine:

Time Machine not configured!
Top Processes by CPU:

18% WindowServer
1% fontd
1% com.apple.WebKit.Networking
0% Safari
0% syslogd
Top Processes by Memory:

567 MB com.apple.WebKit.WebContent
275 MB Safari
180 MB WindowServer
172 MB softwareupdated
69 MB Finder
Virtual Memory Information:

3.76 GB Free RAM
3.09 GB Active RAM
1.15 GB Inactive RAM
584 MB Wired RAM
1.21 GB Page-ins
0 B Page-outs
Diagnostics Information:

Jan 21, 2015, 10:14:50 AM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-21-101450_[redacted].crash
Jan 21, 2015, 10:14:39 AM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-21-101439_[redacted].crash
Jan 21, 2015, 10:14:29 AM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-21-101429_[redacted].crash
Jan 21, 2015, 10:14:18 AM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-21-101418_[redacted].crash
Jan 21, 2015, 10:14:08 AM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-21-101408_[redacted].crash
Jan 21, 2015, 10:13:57 AM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-21-101357_[redacted].crash
Jan 21, 2015, 10:13:38 AM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-21-101338_[redacted].crash
Jan 21, 2015, 06:21:09 AM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-21-062109_[redacted].crash
Jan 21, 2015, 06:17:05 AM Self test - passed
Jan 20, 2015, 07:53:53 PM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-20-195353_[redacted].crash
Jan 20, 2015, 07:53:33 PM /Library/Logs/DiagnosticReports/WindowServer_2015-01-20-195333_[redacted].cpu_resource.diag [Details]
Jan 20, 2015, 07:21:42 PM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-20-192142_[redacted].crash
Jan 20, 2015, 07:21:32 PM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-20-192132_[redacted].crash
Jan 20, 2015, 07:21:22 PM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-20-192122_[redacted].crash
Jan 20, 2015, 07:21:04 PM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-20-192104_[redacted].crash
Jan 21, 2015, 10:13:47 AM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-21-101347_[redacted].crash
Jan 21, 2015, 10:12:07 AM /Library/Logs/DiagnosticReports/WindowServer_2015-01-21-101207_[redacted].crash
Jan 20, 2015, 07:53:54 PM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-20-195354_[redacted].crash
Jan 20, 2015, 07:21:12 PM /Users/[redacted]/Library/Logs/DiagnosticReports/fontd_2015-01-20-192112_[redacted].crash
Jan 20, 2015, 07:16:18 PM /Library/Logs/DiagnosticReports/WindowServer_2015-01-20-191618_[redacted].cpu_resource.diag [Details]