Windows 7 Keeps Crashing

Windows 7 won't wake up from sleep so I have to switch off and on. When I do that it takes about six attempts to start. First of all it can't find the HDD. After trying Start Up Repair & Diagnostics, Windows eventually starts and then crashes to a Black Screen. Eventually Windows cranks up and then it lasts for anything between 10 minutes and three hours before a BSOD Crash which is usually 7A Kernel Data Inpage Error.

After some research I discovered a Microsoft Hot Fix No 404474 which I thought might be relevant but I got the Error Message: Hot Fix won't load:Error 40. Not suitable for your computer!!

I have run virus and malware scans and CCleaner and Super Anti Spyware and nothing nasty comes up.

I have resorted to leaving the machine permanently switched on and it has not crashed for about 60 hours.

Help would be appreciated:

Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows 7 Home Premium, Service Pack 1, 64 bit
Processor: Pentium(R) Dual-Core CPU E5300 @ 2.60GHz, Intel64 Family 6 Model 23 Stepping 10
Processor Count: 2
RAM: 4060 Mb
Graphics Card: Intel(R) G41 Express Chipset, 1806 Mb
Hard Drives: C: Total - 461899 MB, Free - 164566 MB;
Motherboard: Dell Inc., 0J190T
Antivirus: avast! Antivirus, Updated and Enabled
Office 2007 Enterprise Edition