|Assuming you had the modules installed properly and all the way down in their slots....|
If the mboard will not boot when the Wintec module is installed by itself, that module is incompatible with being installed in your mboard.
If your mboard DOES boot when the Wintec module is installed by itself, that module is incompatible with being installed along with your old module at the same time in your mboard.
Why do you keep mentioning what Crucial says when you bought a Wintec ram module ?
Crucial has what's generically called a "ram configurator" program - so do many other ram manufacturers and ram distributors, but Wintec does not appear to have that. When a web site does have a "ram configurator", you can use the brand and model, of your brand name computer, or of your motherboard if you have a generic computer, to look up which e.g. Crucial module part numbers will work in your mboard for sure.
Crucial ram for
Lenovo ThinkCentre A57 (Type 9702, 9703, 9704, 9708) Desktop/PC.
If you had bought the 2gb module part number they list it would have worked in your computer for sure, assuming it's compatible with being installed along with your old module.
Instead you bought the Wintec one.
There is only one possible Wintec 2mb AMPX DDR2 800mhz module
800 Mhz 2GB CL5 1.8V 240 2GB 3AXT6400C5-2048
Detailed specs -
16 128Mx8bit 800mhz DDR2 60 pin FBGA components (chips)
This module is tested to run at DDR2 800mhz at latency timimg of 5-5-5-15 at 1.9v. The SPD is programmed to JEDEC standard DDR2 800mhz at latency timimg of 5-5-5-15 at 1.8v.
Performance varies across all models and motherboards, as not all systems can achieve the full PC2-6400 at CAS latency 5-5-5-15
Ram that works in another mboard , or any ram you buy or have lying around, may not work properly, or sometimes, not at all - even if it physically fits and is the right overall type (e.g. SDram, DDR, DDR2, etc.; PCxxxx, xxx mhz) for your mboard. In the worst cases of incompatibilty your mboard WILL NOT BOOT all the way with it installed, and the mboard may not even beep - the ram has to be compatible with the mboard's main chipset, or in the case of recent mboards, compatible with the memory controller built into the cpu.
See response 5 in this for some info about ram compatibility, and some places where you can find out what will work in your mboard for sure:
Correction to that:
Once you know which module ID strings (part numbers) work in your mboard, you can get them from anywhere you like that has ram with those ID strings.
If you have brand name ram, it is usually easy to look up whether it's ID string (part number) is in a list of compatible modules found by using your mboard or brand name system model number.
If the ram is generic, that may be difficult or impossible.
The timing numbers or the CAS latency being different is not a problem, unless the bios sets it wrong, which usually does not happen - the bios will normally auto set the ram timing numbers to the SLOWEST (HIGHEST) timing numbers of all the ram modules installed.
When you have a slower and faster ram modules installed, the bios will auto set all the ram to the slowest speed - in this case, PC2-5300 specs.
Most if not all DDR2 ram slower than PC2-6400 uses 1.8v, the Jedec specified voltage - some PC2-6400 and faster ram has a higher voltage specified for it.
If you mix modules that have a different voltage specified in their SPD chip on the modules, by default the bios will set the voltage to the LOWEST voltage of all the modules - in that case, the modules that the higher voltage is specified for may not work properly.
In this case, the Wintec module will work fine at either 1.8v or 1.9v, and the SPD chip on it specifies 1.8v, so that probably is not the reason it's incompatible with your mboard.
The Wintec module has 16 chips. Your mboard or cpu may only be compatible with 2gb modules that have 8 chips, or your mboard or cpu may not be able recognize the way the memory is organized on the Wintec module's chips.