Plantages graves réguliers windows 7

bonjour et SOS,

Mon PC plante à n'importe quel moment : en jeu, au démarrage, sur le bureau (alors que je ne fais rien avec)... bref n'importe quand !
Soit j'ai droit à un écran bleu, soit le PC fige (seule solution : couper avec le bouton sur l'UC).
Il a des problèmes pour démarrer : windows ne veut pas se lancer parfois.

rapport de whocrashed :

computer name: BELGARIADE
windows version: Windows 7 Service Pack 1, 6.1, build: 7601
windows dir: C:\Windows
CPU: AuthenticAMD AMD Phenom(tm) II X4 830 Processor AMD586, level: 16
4 logical processors, active mask: 15
RAM: 4294238208 total
VM: 2147352576, free: 1926176768


Crash Dump Analysis


Crash dump directory: C:\Windows\Minidump

Crash dumps are enabled on your computer.


On Wed 7/20/2011 8:18:41 AM GMT your computer crashed
crash dump file: C:\Windows\Minidump\072011-23587-01.dmp
This was probably caused by the following module: ntoskrnl.exe (nt+0x7FD00)
Bugcheck code: 0xFC (0xFFFFF88002F68538, 0x80000000A97EE963, 0xFFFFF80000B9C270, 0x0)
Error: ATTEMPTED_EXECUTE_OF_NOEXECUTE_MEMORY
file path: C:\Windows\system32\ntoskrnl.exe
product: Microsoft® Windows® Operating System
company: Microsoft Corporation
description: NT Kernel & System
Bug check description: This indicates that an attempt was made to execute non-executable memory.
This might be a case of memory corruption. More often memory corruption happens because of software errors in buggy drivers, not because of faulty RAM modules. There is a possibility this problem was caused by a virus or other malware.
The crash took place in the Windows kernel. Possibly this problem is caused by another driver which cannot be identified at this time.


On Wed 7/20/2011 8:18:41 AM GMT your computer crashed
crash dump file: C:\Windows\memory.dmp
This was probably caused by the following module: ntkrnlmp.exe (nt!KeBugCheckEx+0x0)
Bugcheck code: 0xFC (0xFFFFF88002F68538, 0x80000000A97EE963, 0xFFFFF80000B9C270, 0x0)
Error: ATTEMPTED_EXECUTE_OF_NOEXECUTE_MEMORY
Bug check description: This indicates that an attempt was made to execute non-executable memory.
This might be a case of memory corruption. More often memory corruption happens because of software errors in buggy drivers, not because of faulty RAM modules. There is a possibility this problem was caused by a virus or other malware.
The crash took place in the Windows kernel. Possibly this problem is caused by another driver which cannot be identified at this time.


On Wed 7/20/2011 1:29:57 AM GMT your computer crashed
crash dump file: C:\Windows\Minidump\072011-15428-01.dmp
This was probably caused by the following module: ntoskrnl.exe (nt+0x7FD00)
Bugcheck code: 0x3B (0xC0000005, 0xFFFFF80002ADD402, 0xFFFFF88008BBC7B0, 0x0)
Error: SYSTEM_SERVICE_EXCEPTION
file path: C:\Windows\system32\ntoskrnl.exe
product: Microsoft® Windows® Operating System
company: Microsoft Corporation
description: NT Kernel & System
Bug check description: This indicates that an exception happened while executing a routine that transitions from non-privileged code to privileged code.
This appears to be a typical software driver bug and is not likely to be caused by a hardware problem.
The crash took place in the Windows kernel. Possibly this problem is caused by another driver which cannot be identified at this time.


On Tue 7/19/2011 7:36:42 AM GMT your computer crashed
crash dump file: C:\Windows\Minidump\071911-18564-01.dmp
This was probably caused by the following module: ntoskrnl.exe (nt+0x7FD00)
Bugcheck code: 0x3B (0xC0000005, 0xFFFFF80002A96C62, 0xFFFFF880028CFFD0, 0x0)
Error: SYSTEM_SERVICE_EXCEPTION
file path: C:\Windows\system32\ntoskrnl.exe
product: Microsoft® Windows® Operating System
company: Microsoft Corporation
description: NT Kernel & System
Bug check description: This indicates that an exception happened while executing a routine that transitions from non-privileged code to privileged code.
This appears to be a typical software driver bug and is not likely to be caused by a hardware problem.
The crash took place in the Windows kernel. Possibly this problem is caused by another driver which cannot be identified at this time.


Conclusion


4 crash dumps have been found and analyzed.
Read the topic general suggestions for troubleshooting system crashes for more information.

Note that it's not always possible to state with certainty whether a reported driver is actually responsible for crashing your system or that the root cause is in another module. Nonetheless it's suggested you look for updates for the products that these drivers belong to and regularly visit Windows update or enable automatic updates for Windows. In case a piece of malfunctioning hardware is causing trouble, a search with Google on the bug check errors together with the model name and brand of your computer may help you investigate this further.



mais il ne repère pas tous les crash (quand le pc fige notamment)
j'ai vérifié la mémoire avec memtest, nettoyer avec ccleaner, le disque dur a déjà été reformaté. J'ai analysé avec spybot et avast.

J'ai vérifié si les pilotes étaient à jour via le site "touslesdrivers" et ils le sont tous (sauf un audio realtek qui refuse de s'installer au redémarrage demandé.

Mais il plante tous les jours !

Je précise que j'ai un niveau informatique peu élevé.

Merci d'avance

Ma config :
ordinateur HP G5225
windows 7 édition familiale premium 64 bits
carte graphique : ATI Radeon HD 5450
AMD Phenom II X4 830 Processor 2,80 GHz
4 Go DDR3 SDRAM 1333
DD de 1To