Hard drive or Motherboard failure? (linux)

Hello folks.
My PC appears to be dying. Or maybe it's just one of my drives.

Recently, the system drive failed. Or at least, I think it failed. Smart status wasn't good, and it refused to boot. It was also the oldest disk in the machine.

After I replaced it with a new one, everything seemed perfect for about a week. Then another drive started to fail. Read/write operations seemed to be taking longer and longer. I tried unsuccessfully to back up data from it.

I've disconnected that drive, but still more problems. The system simply refuses to boot at the moment. It gets through POST just fine and brings up GRUB. But following OS selection, it stalls endlessly trying to boot it, while repeating a variety of errors, such as:

Code:

[49319.768031] ata6: SRST failed (errno=-16)

Sometimes it also complains about "SATA link down" or various I/O errors

I've disconnected all drives except the brand new system disk, and the problem still isn't going away. This drive is less than a month old and as far as I can tell, the SMART readouts look bad

Code:

ubuntu@ubuntu:~$ sudo smartctl -a /dev/sda
smartctl version 5.38 [i686-pc-linux-gnu] Copyright (C) 2002-8 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

=== START OF INFORMATION SECTION ===
Device Model:     Hitachi HDS721050CLA362
Serial Number:    JPB540HA0XYXUB
Firmware Version: JP2OA3EA
User Capacity:    500,107,862,016 bytes
Device is:        Not in smartctl database [for details use: -P showall]
ATA Version is:   8
ATA Standard is:  ATA-8-ACS revision 4
Local Time is:    Sun Sep  5 13:47:51 2010 UTC
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

General SMART Values:
Offline data collection status:  (0x82)	Offline data collection activity
					was completed without error.
					Auto Offline Data Collection: Enabled.
Self-test execution status:      (   0)	The previous self-test routine completed
					without error or no self-test has ever 
					been run.
Total time to complete Offline 
data collection: 		 (4831) seconds.
Offline data collection
capabilities: 			 (0x5b) SMART execute Offline immediate.
					Auto Offline data collection on/off support.
					Suspend Offline collection upon new
					command.
					Offline surface scan supported.
					Self-test supported.
					No Conveyance Self-test supported.
					Selective Self-test supported.
SMART capabilities:            (0x0003)	Saves SMART data before entering
					power-saving mode.
					Supports SMART auto save timer.
Error logging capability:        (0x01)	Error logging supported.
					General Purpose Logging supported.
Short self-test routine 
recommended polling time: 	 (   1) minutes.
Extended self-test routine
recommended polling time: 	 (  81) minutes.
SCT capabilities: 	       (0x003d)	SCT Status supported.
					SCT Feature Control supported.
					SCT Data Table supported.

SMART Attributes Data Structure revision number: 16
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x000b   100   100   016    Pre-fail  Always       -       0
  2 Throughput_Performance  0x0005   135   135   054    Pre-fail  Offline      -       98
  3 Spin_Up_Time            0x0007   130   130   024    Pre-fail  Always       -       196 (Average 156)
  4 Start_Stop_Count        0x0012   100   100   000    Old_age   Always       -       63
  5 Reallocated_Sector_Ct   0x0033   100   100   005    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x000b   100   100   067    Pre-fail  Always       -       0
  8 Seek_Time_Performance   0x0005   140   140   020    Pre-fail  Offline      -       30
  9 Power_On_Hours          0x0012   100   100   000    Old_age   Always       -       589
 10 Spin_Retry_Count        0x0013   100   100   060    Pre-fail  Always       -       0
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       63
192 Power-Off_Retract_Count 0x0032   100   100   000    Old_age   Always       -       63
193 Load_Cycle_Count        0x0012   100   100   000    Old_age   Always       -       63
194 Temperature_Celsius     0x0002   142   142   000    Old_age   Always       -       42 (Lifetime Min/Max 20/46)
196 Reallocated_Event_Count 0x0032   100   100   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0022   100   100   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0008   100   100   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x000a   200   200   000    Old_age   Always       -       0

SMART Error Log Version: 0
No Errors Logged

SMART Self-test log structure revision number 1
No self-tests have been logged.  [To run self-tests, use: smartctl -t]


SMART Selective self-test log data structure revision number 1
 SPAN  MIN_LBA  MAX_LBA  CURRENT_TEST_STATUS
    1        0        0  Not_testing
    2        0        0  Not_testing
    3        0        0  Not_testing
    4        0        0  Not_testing
    5        0        0  Not_testing
Selective self-test flags (0x0):
  After scanning selected spans, do NOT read-scan remainder of disk.
If Selective self-test is pending on power-up, resume after 0 minute delay.

All the old age and pre-fail flags worry me, considering the very short lifetime of the drive thus far. It seems unfit for purpose to me. Should I return it and get a refund?

Now, in addition to these potential smart issues, there is the beeping. My PC beeps roughly once per second at all times it's turned on, starting about two weeks ago. Every time it beeps, the hard drive access light flashes too.

My motherboard is an Asus a8n-sli SE. I also have an AMD Athlon 64 X2 Dual Core Processor 3800+ in case it's relevant (probably not)

It's pretty obvious something is going horribly wrong. I'm looking for help and advice in diagnosing the issue, so I can avoid wasting money on unnecessary replacements.