Periodic BSOD have been appearing

No antivirus?

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Make scans with these tools -

• TDSSKiller Rootkit Removal Utility Free Download | Kaspersky Lab US
• Online Virus Scanner Eset

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Microsoft Security Essentials & the Free version of Malwarebytes, update and make full scans separately:

• Uninstallers (removal tools) for common antivirus software - ESET Knowledgebase
• Help protect your PC with Microsoft Security Essentials
• Malwarebytes Free

   Note

Do not start the trial version of MalwareBytes

You may also take a look at:

• Good & Free System Security Combination

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Reduce the start-up items, Antivirus software is basically whats required.

• Remove Startup Programs in Windows 7
• Clean Startup in Windows 7

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Run the System File Checker that scans the of all protected Windows 7 system files and replaces incorrect corrupted, changed/modified, or damaged versions with the correct versions if possible:

• Click on the
• Type CMD on Search
• Left click and Run as Administrator
• Type SFC /scannow - read here

Run Disk Check on your Hard Drive for file system errors and bad sectors on it - read here
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Upload a screenshot using:

• CrystalDiskInfo For how to upload a screenshot or file, read here

Test your Hard Drive(s) by running:

• Hard Drive Diagnostic Procedure

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Test and Diagnose RAM Issues with Memtest86+:

• RAM - Test with Memtest86+

   Tip

• Pay close attention to Part 3 of the tutorial "If you have errors"
• Test the RAM with Memtest86+ for at least 7-10 passes. It may take up to 22 passes to find problems. Make sure to run it once after the system has been on for a few hours and is warm, and then also run it again when the system has been off for a few hours and is cold.

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Update Broadcom drivers to its latest.

• Driver Reference Table

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Monitor hardware temperature with system monitoring software like Speccy or HWMonitor. Upload a screen shot of the Summary tab as well:

• Piriform - Speccy
• CPUID - HWMonitor

• For how to upload a screenshot or file, read here

Good luck.