Windows Vista: Pc stürzt ab, Bluescreen, Fährt nicht mehr hoch

Guten Morgen
ich hoffe ihr könnt mir etwas weiterhelfen. ..
schon mal Vielen Dank!
Mein Problem:
Mein Computer stürtzt immer ab und es erscheint ein Bluescreen mit einer Fehlermeldung.
Meist fährt der PC dann auch nicht mehr hoch.
Wo könnte das Problem liegen?


Mein Computer-System:
Prozessor: Intel(R) Pentium(R) D CPU 3,00 GHz 2,99 GHz
Arbeitsspeicher (RAM):  2047 MB
Windows Vista Ultimate 64 bit
Grafikkarte:  NVIDIA GeForce 8600 GT   
Mein PC ist etwa 2 Jahre alt.


Fehlermeldungen:
1)
A problem has been detected and windows has been shut down to prevent damage
to your computer.
irql_not_less_or_equal
if this is the first time you`ve seen this stop error screen,
restart your computer. If this screen appears again, follow
these steps:

Check to make sure any new hardware or software is properly installed.
If this is a new installation, ask your hardware or software manufacturer
for any windows updates you might need.

If problems continue, disable or remove any newly installed hardware
or software, disable BIOS memory optionssuch as caching or shadowing
if you need to use safe Mode to remove or disable components, restart
your computer, press F8 to select Advanced startup Options, and then
select Safe Mode.

Technical Information:
"""STOP: 0x0000000A (0x0000010000FFFFFA, 0x000000000000000C, 0x0000000000000001, 0
xFFFFF80002050E1E)


Collecting date for crash dump . . .
Initializing disk for crash dump. . .
Beginning dump of physical memory.
Dumping physical memory to disk: 100


2)
A problem has been detected and windows has been shut down to prevent damage
to your computer.

if this is the first time you`ve seen this stop error screen,
restart your computer. If this screen appears again, follow
these steps:

Check to be sure you have adequate disk space. If a driver is
identified in the stop message, disable the driver or check
with the manufacturer for driver updates. Try changing video
adapters.

Check with your hardware vendor for any BIOS updates. Disable
BIOS memory options such as caching or shadowing. If you need
to use Safe Mode to remove or disable components, restart your
computer, press F8 to select Advanced Startup Options, and then
select Safe Mode.

Technical Information:
"""STOP: 0x0000007E (0xFFFFFFFFC0000005, 0xFFFFF9800024961E, 0xFFFFF98000A06098,
0xFFFFF98000A05A70)

"""      acpi.sys  - Address  FFFFF9800024961E base at FFFFF9800023C000, DateStamp
4549b5ec


3)
STOP: C0000221 Unknown Hard Error
\SystemRoot\System32?ntdll.dll

Collecting date for crash dump . . .
Initializing disk for crash dump. . .
Beginning dump of physical memory.
Dumping physical memory to disk: 70

Gruß
Max