Why Windows Won't Start After RAM Replacement

The main issue is voltage incompatibility of the RAM. Your Acer TravelMate 5742ZG laptop with an Intel Pentium P6100 processor, released in 2011, is designed to work with DDR3 memory at 1.5V voltage, while you installed DDR3L modules at 1.35V voltage. Although DDR3L should theoretically work at 1.5V, in your case it causes conflicts in the memory controller, limiting the recognizable capacity to 2GB or causing system boot failure.

Table of Contents

• Main Causes of the Problem
• Analysis of DDR3 and DDR3L Compatibility
• Solution to the Problem
• RAM Selection Recommendations
• Step-by-Step Action Plan

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Main Causes of the Problem

The problem arises from several key factors related to your system’s compatibility with the installed memory:

1. Voltage Mismatch: Your laptop expects DDR3 memory at 1.5V, while the installed Samsung modules operate at 1.35V (DDR3L). Although DDR3L should theoretically be backward compatible, in practice it causes issues with the Intel Pentium P6100 processor’s memory controller.

2. Processor Limitations: Research shows that the Pentium P6100 processor may have limitations when working with DDR3L memory, especially when using two modules simultaneously. The memory controller (IMC) in such processors may not correctly process signals from low-voltage modules.

3. Capacity Recognition Issues: The system partially recognizes the memory (up to 2GB), which indicates that the modules are physically working, but the memory controller cannot properly handle the full capacity due to the voltage conflict.

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Analysis of DDR3 and DDR3L Compatibility

From research on RAM compatibility, the following important points can be highlighted:

Important: DDR3L (1.35V) is only theoretically backward compatible with DDR3 (1.5V). In practice, many systems, especially older models, may experience serious problems.

According to research, there are three main interaction scenarios:

1. DDR3L in a DDR3 slot: Generally, DDR3L modules can work in DDR3 slots, switching to 1.5V voltage. However, this doesn’t always happen correctly.

2. DDR3 in a DDR3L slot: This doesn’t work, as DDR3 modules cannot operate at the reduced 1.35V voltage.

3. Mixed configurations: Using different types of memory in one laptop almost always leads to problems.

In your case, according to research data, the system partially works, which confirms the possibility of DDR3L working in your laptop, but with serious limitations.

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Solution to the Problem

Option 1: Using Only DDR3 Memory (1.5V)

The most reliable way to solve the problem is to replace the installed DDR3L modules with DDR3 at 1.5V. According to research, your laptop officially supports up to 8GB of DDR3 memory.

Recommendation: Look for DDR3 SODIMM PC3-10600 or PC3-12800 with 1.5V voltage and timings compatible with your system.

Option 2: Checking and Updating BIOS

Sometimes the problem may be related to an outdated BIOS version:

1. Check the current BIOS version on the official Acer website
2. If necessary, update BIOS to the latest version
3. After updating, try reinstalling the memory

Option 3: Using a Single DDR3L Module

If you want to keep the DDR3L memory, try using only one 4GB module. Some systems work better with a single module than with two.

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RAM Selection Recommendations

Based on compatibility research for your laptop model, the following is recommended:

Important: Avoid memory with 1.35V voltage (DDR3L) for your system, as it causes problems with your processor’s memory controller.

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Step-by-Step Action Plan

1. Return to Original Configuration: Reinstall the original 2GB DDR3 1.5V Kingston module to confirm system functionality.

2. Purchase Correct Memory: Buy two DDR3 1.5V PC3-10600 or PC3-12800 modules, each 4GB in capacity.

3. Test New Memory: Before installing in the laptop, test the memory on another compatible device or use a test bench.

4. Install Memory: Install both new modules in the laptop slots, following the correct sequence.

5. Configure BIOS: Check BIOS settings related to memory and, if necessary, reset settings to default values.

6. Install Windows 7: If the system doesn’t boot, you may need to reinstall Windows 7 with 8GB RAM support.

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Sources

1. RAM Upgrades | TravelMate 5742Z / 5742ZG - max up to 8GB
2. RAM upgrade from 2GB to 8GB for Acer Aspire 5742 - Acer Community
3. Arbeitsspeicher RAM | Acer Aspire 5742 (5742G, 5742Z, 5742ZG)
4. Acer Aspire 5742 Memory Upgrade - Acer 5742 Aspire Laptop Memory
5. Can I add to my laptop a DDR3L RAM of 1.35v if I already have a DDR3 RAM of 1.5v configured to run at 1.35v? - Super User
6. 1.35 V RAM in a 1.5 V system - Will it fry or overclock? - Super User
7. Can I use 1.5v ram in a slot which manufacturer recommends 1.35V? - Tom’s Hardware Forum
8. 1.35v - 1.5v dual-voltage DDR3 memory | Crucial.com

Conclusion

The main cause of the problem is the use of DDR3L memory (1.35V) in a laptop designed to work with DDR3 (1.5V). To solve the problem, you need to:

1. Replace the installed DDR3L modules with DDR3 memory at 1.5V voltage
2. Select memory with PC3-10600 or PC3-12800 specifications
3. If necessary, update BIOS to the latest version
4. Thoroughly test the system after installing new memory

Even though DDR3L should theoretically be backward compatible, in practice many older systems, especially with Intel processors of that generation, have limitations when working with low-voltage memory. Investing in the correct DDR3 memory (1.5V) will guarantee stable operation of your system with the full 8GB of RAM.